Integrating headers from upstream registry [0] master branch. Effective
GL registry commit integrated:

9d534f9312e56c72df763207e449c6719576fd54

Keeping the following quirks local to Mesa:

- glext.h: BUILDING_MESA guard (see !1492)

- glxext.h: glXQueryGLXPbufferSGIX: 'int' return type (Mesa) vs while
'void' (GL registry)

- glxext.h: GLX_RENDERER_ID_MESA is still expected by some mesa tests,
even though its token has been removed from the spec (see
docs/specs/MESA_query_renderer.spec)

- glxext.h: glXGetTransparentIndexSUN / PFNGLXGETTRANSPARENTINDEXSUNPROC
argument pTransparentIndex has type 'unsigned long *' (Mesa) vs. 'long
*' (GL registry)

[0] https://github.com/KhronosGroup/OpenGL-Registry



Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>