diff --git a/core/HTTP.php b/core/HTTP.php
index dc20b963b..4590076b2 100644
--- a/core/HTTP.php
+++ b/core/HTTP.php
@@ -5,10 +5,10 @@
  * Like Debug, this is more a bundle of methods than a class ;-)
  */
 class HTTP {
-	
+
 	static $userName;
 	static $password;
-	
+
 	/**
 	 * Turns a local system filename into a URL by comparing it to the script filename
 	 */
@@ -21,29 +21,29 @@ class HTTP {
 				break;
 			}
 		}
-		
+
 		$urlBase = substr($_SERVER['PHP_SELF'], 0, -(strlen($_SERVER['SCRIPT_FILENAME']) - $commonLength));
 		$url = $urlBase . substr($filename, $commonLength);
 		$protocol = $_SERVER['HTTPS'] ? "https" : "http";
 		return "$protocol://". $_SERVER['HTTP_HOST'] . $url;
-		
+
 		// Count the number of extra folders the script is in.
 		// $prefix = str_repeat("../", substr_count(substr($_SERVER[SCRIPT_FILENAME],$commonBaseLength)));
 	}
-	
+
 	/**
 	 * Turn all relative URLs in the content to absolute URLs
 	 */
 	static function absoluteURLs($html) {
 		return HTTP::urlRewriter($html, '(substr($URL,0,1) == "/") ? ( Director::protocolAndHost() . $URL ) : ( (ereg("^[A-Za-z]+:", $URL)) ? $URL : Director::absoluteBaseURL() . $URL )' );
 	}
-	
+
 	/*
 	 * Rewrite all the URLs in the given content, evaluating the given string as PHP code
 	 *
 	 * Put $URL where you want the URL to appear, however, you can't embed $URL in strings
 	 * Some example code:
-	 *  '"../../" . $URL' 
+	 *  '"../../" . $URL'
 	 *  'myRewriter($URL)'
 	 *  '(substr($URL,0,1)=="/") ? "../" . substr($URL,1) : $URL'
 	 */
@@ -52,107 +52,107 @@ class HTTP {
 		foreach($attribs as $tag => $attrib) {
 			if(!is_numeric($tag)) $tagPrefix = "$tag ";
 			else $tagPrefix = "";
-	
+
 			$regExps[] = "/(<{$tagPrefix}[^>]*$attrib *= *\")([^\"]*)(\")/ie";
 			$regExps[] = "/(<{$tagPrefix}[^>]*$attrib *= *')([^']*)(')/ie";
 			$regExps[] = "/(<{$tagPrefix}[^>]*$attrib *= *)([^\"' ]*)( )/ie";
 		}
 		$regExps[] = '/(background-image:[^;]*url *\()([^)]+)(\))/ie';
 		$regExps[] = '/(background:[^;]*url *\()([^)]+)(\))/ie';
-	
-		// Make 
+
+		// Make
 		$code = 'stripslashes("$1") . (' . str_replace('$URL', 'stripslashes("$2")', $code) . ') . stripslashes("$3")';
-	
+
 		foreach($regExps as $regExp) {
 			$content = preg_replace($regExp, $code, $content);
 		}
-			
-		return $content;		
+
+		return $content;
 	}
-	
+
 	static function setGetVar($varname, $varvalue, $currentURL = null) {
 		$currentURL = $currentURL ? $currentURL : $_SERVER['REQUEST_URI'];
-		
+
 		$scriptbase = $currentURL;
 		$scriptbase = str_replace('&amp;','&',$scriptbase);
-		
+
 		$scriptbase = ereg_replace("&$varname=[^&]*",'',$scriptbase);
 		$scriptbase = ereg_replace("\?$varname=[^&]*&",'?',$scriptbase);
 		$scriptbase = ereg_replace("\?$varname=[^&]*",'',$scriptbase);
-		
+
 		$suffix = '';
 		if(($hashPos = strpos($scriptbase,'#')) !== false) {
 			$suffix .= substr($scriptbase, $hashPos);
 			$scriptbase = substr($scriptbase, 0, $hashPos);
 		}
-		
+
 		if($varvalue !== null) {
 			$scriptbase .= (strrpos($scriptbase,'?') !== false) ? '&' : '?';
 			$scriptbase .= "$varname=" . (isset($urlEncodeVarValue) ? urlencode($varvalue) : $varvalue);
 		}
-	
+
 		$scriptbase = str_replace('&','&amp;',$scriptbase);
 		return $scriptbase . $suffix;
 	}
-	
+
 	static function RAW_setGetVar($varname, $varvalue, $currentURL = null) {
 		$url = self::setGetVar($varname, $varvalue, $currentURL);
 		return Convert::xml2raw($url);
 	}
-	
+
 	static function findByTagAndAttribute($content, $attribs) {
-		
+
 		foreach($attribs as $tag => $attrib) {
 			if(!is_numeric($tag)) $tagPrefix = "$tag ";
 			else $tagPrefix = "";
-	
+
 			$regExps[] = "/(<{$tagPrefix}[^>]*$attrib *= *\")([^\"]*)(\")/ie";
 			$regExps[] = "/(<{$tagPrefix}[^>]*$attrib *= *')([^']*)(')/ie";
 			$regExps[] = "/(<{$tagPrefix}[^>]*$attrib *= *)([^\"' ]*)( )/ie";
 		}
-	
+
 		foreach($regExps as $regExp) {
 			$content = preg_replace($regExp, '$items[] = "$2"', $content);
 		}
-		
+
 		return isset($items) ? $items : null;
 	}
-	
+
 	static function getLinksIn($content) {
 		return self::findByTagAndAttribute($content, array("a" => "href"));
 	}
 	static function getImagesIn($content) {
 		return self::findByTagAndAttribute($content, array("img" => "src"));
 	}
-	
+
 	/*
 	 * Outputs appropriate header for downloading a file
 	 * exits() after the call, so that no further output is given
 	 */
-	static function sendFileToBrowser($fileData, $fileName, $mimeType = false) {	
+	static function sendFileToBrowser($fileData, $fileName, $mimeType = false) {
 		if(!$mimeType) $mimeType = self::getMimeType($fileName);
 		$ext = strtolower(substr($fileName,strrpos($fileName,'.')+1));
 		$inlineExtensions = array('pdf','png','jpg','jpe','gif','swf','htm','html','txt','text','avi','wmv','mov','mpe','mpg','mp3','mpeg');
-		
+
 		if(in_array($ext, $inlineExtensions)) $inline = true;
-		
+
 		header("Content-Type: $mimeType; name=\"" . addslashes($fileName) . "\"");
-		//header("Content-Type: $mimeType" );	
-		// Downloadable		
+		//header("Content-Type: $mimeType" );
+		// Downloadable
 		//if(!$inline)
 			$dispHeader = "Content-disposition: attachment; filename=" . addslashes($fileName) . "";
-		
+
 		// Debug::message('CD: ' . strlen( $dispHeader ) );
-		
-		
-		header( $dispHeader );		
+
+
+		header( $dispHeader );
 		header("Content-Length: " . strlen($fileData));
-		
+
 		echo $fileData;
-	
+
 		exit();
 	}
-	
+
 	/*
 	 * Get mime type based on extension
 	 */
@@ -162,7 +162,7 @@ class HTTP {
 		$ext = strtolower(substr($filename,strrpos($filename,'.')+1));
 		return $global_mimetypes[$ext];
 	}
-	
+
 	/*
 	 * Load the mime-type data from the system file
 	 */
@@ -181,7 +181,7 @@ class HTTP {
 					}
 				}
 			}
-		
+
 		// Fail-over for if people don't have /etc/mime.types on their server.  it's unclear how important this actually is
 		} else {
 			$mimeData = array(
@@ -190,104 +190,111 @@ class HTTP {
 				"rtf" => "application/rtf",
 			);
 		}
-	
+
 		global $global_mimetypes;
 		$global_mimetypes = $mimeData;
 		return $mimeData;
 	}
-	
+
 	/**
 	 * Send an HTTP request to the host
 	 */
 	static function sendRequest( $host, $path, $query, $port = 80 ) {
 		$socket = fsockopen( $host, $port, $errno, $error );
-		
+
 		if( !$socket )
 			return $error;
-			
+
 		if( $query )
 			$query = '?' . $query;
-			
+
 		if( self::$userName && self::$password ) {
 			$auth = "Authorization: Basic " . base64_encode( self::$userName . ':' . self::$password ) . "\r\n";
 		} else {
 			$auth = '';
 		}
-		
+
 		$request = "GET {$path}{$query} HTTP/1.1\r\nHost: $host\r\nConnection: Close\r\n{$auth}\r\n";
-		
+
 		fwrite( $socket, $request );
 		$response = stream_get_contents( $socket );
-		
+
 		return $response;
 	}
-	
+
 	static function sendPostRequest( $host, $path, $data, $name, $query = '', $port = 80 ) {
 
 		$socket = fsockopen( $host, $port, $errno, $error );
-		
+
 		if( !$socket )
 			return $error;
-			
+
 		if( self::$userName && self::$password )
 			$auth = "Authorization: Basic " . base64_encode( self::$userName . ':' . self::$password ) . "\r\n";
-			
+
 		if( $query )
 			$query = '?' . $query;
 
 		$data = urlencode( $data );
 		$data = $name . '=' . $data;
-		$length = strlen( $data );	
-		
+		$length = strlen( $data );
+
 		$request = "POST {$path}{$query} HTTP/1.1\r\nHost: $host\r\n{$auth}Content-Type: application/x-www-form-urlencoded\r\nContent-Length: $length\r\n\r\n";
-		
+
 		$request .= $data . "\r\n\r\n";
-		
+
 		fwrite( $socket, $request );
 		$response = stream_get_contents( $socket );
-		
+
 		/*if( $query )
 			$query = '?' . $query;
-			
-		$vars['synchronise'] = $data;	
-			
+
+		$vars['synchronise'] = $data;
+
 		$curl = curl_init('http://' . $host . $path );
-		
+
 		curl_setopt( $curl, CURLOPT_RETURNTRANSFER, 1);
 		curl_setopt( $curl, CURLOPT_POSTFIELDS, $vars );
 		curl_setopt( $curl, CURLOPT_POST, 1 );
 		curl_setopt( $curl, CURLOPT_VERBOSE, true );
 		curl_setopt( $curl, CURLOPT_USERPWD, self::$userName . ':' . self::$password);
-		
+
 		$response = curl_exec( $curl );
 		curl_close( $curl );*/
-		
+
 		return $response;
-		
+
 	}
-	
+
 	protected static $cache_age = 86400, $modification_date;
-	
+
 	/**
 	 * Set the maximum age of this page in web caches, in seconds
 	 */
 	static function set_cache_age($age) {
 		self::$cache_age = $age;
 	}
-	
+
 	static function register_modification_date($dateString) {
 		$timestamp = strtotime($dateString);
 		if($timestamp > self::$modification_date) self::$modification_date = $timestamp;
 	}
-	
+
+	static function register_modification_timestamp($timestamp) {
+		if($timestamp > self::$modification_date)
+			self::$modification_date = $timestamp;
+	}
+
 	/**
 	 * Add the appropriate caching headers to the response
+	 *
+	 * @param string The reponse body
 	 */
-	static function add_cache_headers() {
+	static function add_cache_headers($body = null) {
 		// Development sites have frequently changing templates; this can get stuffed up by the code
 		// below.
 		if(Director::isDev()) return;
-		
+
 		if(!headers_sent()) {
 			if(function_exists('apache_request_headers')) {
 				$headers = apache_request_headers();
@@ -295,34 +302,34 @@ class HTTP {
             // bdc: now we must check for DUMB IE6:
             if(isset($headers['x-requested-with']) && $headers['x-requested-with'] == 'XMLHttpRequest') self::$cache_age = 0;
 			}
-			
+
 			if(self::$cache_age > 0) {
 				header("Cache-Control: max-age=" . self::$cache_age . ", must-revalidate");
 				header("Pragma:");
 			} else {
 				header("Cache-Control: no-cache, max-age=0, must-revalidate");
 			}
-			
+
 			if(self::$modification_date && self::$cache_age > 0) {
 				header("Last-Modified: " . self::gmt_date(self::$modification_date));
-				
+
 				$expires = 2 * time() - self::$modification_date;
 				header("Expires: " . self::gmt_date($expires));
 			}
 		}
 	}
 
+
 	/**
-	 * Return an RFC 2822 date in the GMT timezone
-	 */	
+	 * Return an {@link http://www.faqs.org/rfcs/rfc2822 RFC 2822} date in the
+	 * GMT timezone (a timestamp is always in GMT: the number of seconds
+	 * since January 1 1970 00:00:00 GMT)
+	 */
 	static function gmt_date($timestamp) {
-			// Get the timezone offset in seconds
-			$timezone = date('O');
-			$timezoneOffset = (($timezone[0] == '-')?-1:1) * (substr($timezone,1,2)*3600) + (substr($timezone,3,2)*60);
-			
-			return date('D d M Y h:i:s', $timestamp - $timezoneOffset) . ' GMT (' . $timezoneOffset . ')';
+		return gmdate('D, d M Y H:i:s', $timestamp) . ' GMT';
 	}
-		
+
 }
 
-?>
+
+?>
\ No newline at end of file