Caches for wikis with table prefixes will be lost on upgrade, caches for wikis without table prefixes will be preserved. Custom cache keys in extensions can be migrated at leisure. Extensions which write to core cache keys should be migrated ASAP, as I have done with Special:Makesysop.
* Deleted DatabaseMysql.php, no longer necessary, database classes are autoloaded.
* Moved wfGetMimeMagic() to MimeMagic::singleton()
* Fixed a couple of __CLASS__.'::'.__FUNCTION__ things.