[Beignet] Status of cl_khr_gl_sharing

[Rebecca N. Palmer]

The *missing* functions aren't likely to be a problem: as far as I can 
tell, 
http://sources.debian.net/src/forge/0.9.2-2/examples/opencl/cl_helpers.h/?hl=72#L72 
is the only place in Debian that tries to use one of them, and it 
correctly handles its absence.

I'm more worried about the potential consequences (if any) of 
clEnqueueAcquire/ReleaseGLObjects not actually doing anything.