* Replaced $wgMessageCache by MessageCache::singleton(); since we only use one instan...

* Replaced $wgMessageCache by MessageCache::singleton(); since we only use one instance of this class (as for ParserCache, LinkCache)
* MessageCache::singleton() calls wfGetMessageCacheStorage() directly instead of using $messageMemc, just in case this would be called before that variable is set
* Per TimStarling: also removed deprecated methods in MessageCache class: addMessages() and related, [get|set|enable|disable]Transform(), loadAllMessages(), loadMessageFile() and some others. Same for the legacyData stuff in LocalisationCache that was only used by MessageCache::addMessages() and related.
* Converted remaining extensions