Bug 895091 - Remove references to C WebVTT parser and unused code r=rillian

- Remove left over references to WebVTT C parser in TextTrackCue and
WebVTTListener classes.
- Remove miscellaneous unused code as well and included libraries as
well.
Bug 895091 - Add WebVTT parser and wrapper IDLs r=rillian, ted, gwagner, khuey

- Added vtt.js, a JS WebVTT parser, to Gecko.
- Added a wrapper to interface between it and Gecko.
- Updated TextTrackCue and WebVTTListener to work with it.

--HG--
rename : content/media/WebVTTLoadListener.cpp => content/media/WebVTTListener.cpp
rename : content/media/WebVTTLoadListener.h => content/media/WebVTTListener.h
Bug 895091 - Add JS WebVTT parser code in (vtt.js) r=rillian, ted, gwagner, khuey

- Current source code for vtt.js can be found at:
https://github.com/andreasgal/vtt.js
- vtt.js code taken from commit 6bca57d265fc58cff091148b426ec69f576057d7.
Bug 895091 - Turn text track cue tests back on r=rillian
Bug 895091 - Test for multiple WebVTT files loading at once r=khuey
Bug 915846 - IonMonkey: Const-qualify some range pointees. r=nbp
Bug 915846 - IonMonkey: Rename things to say "canHaveFractionalPart" instead of "decimal". r=nbp
Bug 914405: Define makeGlobalObjectReference, a quick way to get D.O's referring to global objects, to simplify the web console. r=jorendorff r=msucan
Bug 914405: fix for browser_bug_638949_copy_link_location.js; r=me
Bug 914373 - Verify $PATH is sane during bootstrap; r=mshal
Bug 914372 - Provide more info to help with installing Python; r=mshal
Bug 901278 - More intelligently detect installed Xcode; r=mshal
Bug 910487 - Hack binary Python extensions into building on Windows; r=mshal
Bug 870420 - Require Python 2.7.3+ to build; r=ted
Bug 909602 - Don't blow away most/all elements above the purported "length" of a non-Array object passed to Array.prototype.pop.  r=bhackett
Bug 917576. Parse non-string pref values. r=ahal
Bug 917576. Disable failing crashtest for Cipc. r=bholley
Bug 915735 - Part 0: Stop pulling in all of jsapi.h into gkmedias.dll; rs=bjacob
Back out 813a35c5b24a for ASan failure. r=bustage CLOSED TREE

Only one test is failing (so far) and the feature itself is
behind a pref, so this doesn't affect users.
Backed out changeset feca3867b395 (bug 895091)