* Second try of split message caches with changes suggested by Tim Starling and other small fixes
* removed use of umask, wfMkdirParents works now
* splitting of messages per language is now unconditional
* storing cached messages in 2-d array of code => messages
* fixed a bug in replace(), now deletion works properly
* clear() should actually do something now
* try to delay parser creation in transform()
* removed the use of $memcPrefix and wfMemcKeyLang() in favour of wfMemcKey()
* escape $code in loadFromDb()
* use member variable instead of static variable for tracking loaded languages