Refactor the factory/i18n/list/etc static methods from SpecialPage into their own...

Refactor the factory/i18n/list/etc static methods from SpecialPage into their own class; there's no reason we need to be parsing them in every single SpecialPage subclass.  Leave all the methods as stubs in SpecialPage.php; if we required PHP 5.3 they could be replaced by a a __callStatic() magic method, but that doesn't work on PHP 5.2.

Also make a few changes to the functions available.  SpecialPageFactory::resolveAlias() now takes an optional subpage and returns array(<name>,<subpage>).  Similarly merge getPage() and getPageByAlias().  There were many examples of (extensions particularly) making dubious assumptions about the presence or absence of subpages or canonical-ness.

I didn't deprecate SpecialPage::getTitleFor() as it's got over six hundred calls.  I'm rather undecided on the best position of getPage()/executePath().  Although the latter needs cleanup anyway.