BUG dev/build fails to add extra fields to SiteConfig (fixes #65)

Caused by Translatable->populateSiteConfigDefaults()
triggering before newly created fields are available in the
"SiteConfig" database table.

code/model/Translatable.php

@@ -1198,6 +1198,7 @@ class Translatable extends DataExtension implements PermissionProvider {
 		// When the database is being setup singleton('SiteConfig') is called.
 		if(!DB::getConn()->hasTable($this->owner->class)) return;
 		if(!DB::getConn()->hasField($this->owner->class, 'Locale')) return;
+		if(DB::getConn()->isSchemaUpdating()) return;
 		
 		// Find the best base translation for SiteConfig
 		Translatable::disable_locale_filter();