SDL_opengl: Move glext.h to a separate file.

--HG--
extra : rebase_source : 36b782051e621861bfc8f47249a4e2d1ea8f4775
SDL_opengles2: Separate out GLES2 headers.

--HG--
extra : rebase_source : 67a615ceb77389a2be5ba5177966e3255bdc964b
SDL_opengl: Update to glext.h from Khronos dated 2014-05-21.

This updates to the latest glext.h from Khorons that includes the OpenGL
4.4 specification. It was retrieved from
http://www.opengl.org/registry/api/GL/glext.h at 2014-06-04.

--HG--
extra : rebase_source : 85adb5e14c704f0202041dc0dd9ef9402508f1f6
SDL_opengles2: Update to latest Khronos headers.

This updates to the latest Khronos headers, which gives the latest
headers for MSVC.

The following files were retrieved on 2014-06-04:

http://www.khronos.org/registry/gles/api/GLES2/gl2.h
http://www.khronos.org/registry/gles/api/GLES2/gl2ext.h
http://www.khronos.org/registry/gles/api/GLES2/gl2platform.h
http://www.khronos.org/registry/egl/api/KHR/khrplatform.h

And they were modified to not include each other themselves.

--HG--
extra : rebase_source : 99ed4a21b67a35a11f9af80de79d844ea8ac0d80
Fixed escape cancelling fullscreen mode now that the SDL window is the first res
ponder.