sys/glsink/: Rewrite a bunch of code to use textures as the intermediate instead...

sys/glsink/: Rewrite a bunch of code to use textures as the intermediate instead of renderbuffers.  upload, download,...

Original commit message from CVS:
* sys/glsink/glimagesink.c:
* sys/glsink/glimagesink.h:
* sys/glsink/glvideo.c:
* sys/glsink/glvideo.h:
* sys/glsink/gstglbuffer.c:
* sys/glsink/gstglbuffer.h:
* sys/glsink/gstgldownload.c:
* sys/glsink/gstglfilter.c:
* sys/glsink/gstglupload.c:
Rewrite a bunch of code to use textures as the intermediate
instead of renderbuffers.  upload, download, filtering all
work.