gles2rice: Consolidated custom code and sync with upstream.

A pull request was placed upstream to move the #if SDL_VIDEO_OPENGL in
OGLGraphicsContext.cpp.

The custom code needs to change with this upstream change, so I commit
both the custom and upstream changesets at once to keep things in sync.
Small fix to GL ES 2.0 codepath (less aggressive #ifdef exclusion).
gles2rice: Merge 'upstream/video-rice' hg:e25d038c196cb7c8cd4dd71839f1994c1257b2ae