Drop the default requested OpenGL version to 1.2.

Fixes default context creation on Mac OS X <= 10.6.

--HG--
extra : rebase_source : e8cb3a139e6af51f94929203d1046665e0d2c438
extra : histedit_source : fa77978715a878180315ea637d08d788cee94e93%2C12a503d312aeafe7669f059b1644cb04ce994b82
Turn off Mir support in the buildbot Raspberry Pi script.
Updated WinCE readme to note WinRT work.
Removed unused variable.