HTMLFileCache refactoring:

HTMLFileCache refactoring:
* Rewrote class and split into three classes: a base class, and html cache and a more generic cache to be used later.
* The new classes now use RequestContext.
* Renamed fetchPageText() -> fetchText().
* Split out new saveText() function from saveToFileCache().
* Various other cleanups and fixes.
Also fixed backwards setting of $wgDisableCounters in rebuildFileCache.php.