Various performance and initialisation issues:

Various performance and initialisation issues:
* Made autoloader work for unserialize()
* Made XmlFunctions.php and HttpFunctions.php autoloadable modules, via Http:: and Xml::
* Made Image class autoloadable, global functions moved to ImageFunctions.php where they can be loaded on every invocation.
* Removed some unnecessary require_once() calls
* Deferred $wgValidSkinNames initialisation
* Fixed a couple of silly construct/initialise splits. My idea from C++ experience, bad practice in PHP.
* Deferred skin initialisation in ParserOptions
* Removed $wgMwRedir during an attempt to make MagicWord autoloadable. Didn't complete that, but removing the global is still the right direction.