Bug 625015 - Improve the error message when the X development libraries are not available; r=glandium

Patch based on the one of Aikeremu Tiemuer
Bug 845057 - Part 1: Use DOMSettableTokenList for iframe.sandbox; r=bz
Bug 845057 - Part 2: Tests (sanity checking sandbox DOMSettableTokenList attribute); r=bz
Bug 845057 - Part 3: Use the parsed attribute in ParseSandboxAttributeToFlags; r=bz
Bug 882703 - Add TextTrackList change event; r=rillian,bz
Bug 909914 - Add a missing include to avoid error: "Use of undeclared identifier 'getpid'" when building with enable-macos-target=10.9; r=smichaud
Bug 913665 - Detect minified files and pretty print them by default; r=fitzgen
Bug 921484 - Fix bugs found in TextTrack::GetActiveCues(); r=rillian
* mDirty needs to be set to false after the list has been recomputed.
* The loop that adds cues to the list doesn't work properly when the
  list has become dirty as we check if endTime < playback time and
  since we start from pos 0 we will never get past the first cue.
Bug 935987 - Part 1: Give the preprocessor a better API; r=gps
Bug 948889 - Move the inline script in aboutTabCrashed.xhtml into a separate file; r=ttaubert