[Core JS] wikibits.js / IEFixes clean up

[Core JS] wikibits.js / IEFixes clean up
* fix on-the-loose fixalpha() call
-- Calls should not be dangling loose like that
-- Removed local calls from skins and installer
-- instead calling from the IEFixes script (which is loaded raw by wikibits which is loaded from the bottom, as are all legacy scripts)
* Removing usage of 'skinpath' and 'skin' globals in wikibits.js, those aren't globals per se since introduction of mw.config and $wgLegacyJavaScriptGlobals
* Wrapping wikibits.js in closure to avoid leakage of "local" variables. This shouldn't break anything as it is loaded through resource loader which, in production mode, wraps it in a closure anyway.
* adding explicit posision=>bottom for wikibits. 'bottom' is default but repeating here since it must not change for legacy reasons.