* Removed lots of explicit require_once statements. The autoloader should theoretical...

* Removed lots of explicit require_once statements. The autoloader should theoretically be faster, because it always uses an absolute path, eliminating the need for a search, and it is never called unnecessarily. Absolute paths are also more robust in the face of odd configurations or usage patterns. Moved a few constants around to support this, they always have to be available before the method call.
* Deleted DatabaseMysql.php, no longer necessary, database classes are autoloaded.
* Moved wfGetMimeMagic() to MimeMagic::singleton()
* Fixed a couple of __CLASS__.'::'.__FUNCTION__ things.