[LowLevelGLPaint] _format variable was never used
[LowLevelGLPaint] Update deployment target to 5.1.1 and change SDK version
[LowLevelGLPaint] Remove duplicated using, add new keyword to hide parent method, update All.Clear method to use ClearBufferMask enum instead of uint
Merge branch 'magic-types-migration' of github.com:xamarin/monotouch-samples into magic-types-migration