Changes ping to POST and clears Requirements for ping

GET requests can, and do, get cached. Using POST forces them not to.
Clears requirements so that the SecurityAdmin JS isn't injected.

admin/code/LeftAndMain.php

@@ -403,6 +403,7 @@ class LeftAndMain extends Controller implements PermissionProvider {
 	 * This is used in the CMS.
 	 */
 	public function ping() {
+		Requirements::clear();
 		return 1;
 	}
 	

admin/javascript/LeftAndMain.Ping.js

@@ -40,6 +40,7 @@
 					$.ajax({
 						url: 'admin/security/ping',
 						global: false,
+						type: 'POST',
 						complete: onSessionLost
 					});
 				}, this.getPingIntervalSeconds() * 1000);