We can now do this since we finally switched to PHP 5.3 for MW 1.20 and get rid of the silly dirname(__FILE__) stuff :)
Change-Id: Id9b2c9cd2e678197aa81c78adced5d1d31ff57b1
* Use default .cache extension for ResourceFileCache. No need for js/css extension, and makes extension sanity check in prune script simpler.
* Removed redundant setting of mExt in ObjectFileCache