Merge branch 'shader-file-reorg'

Merge branch 'shader-file-reorg'

1. Move all GL entrypoint functions and files into src/mesa/main/
This includes the ARB vp/vp, NV vp/fp, ATI fragshader and GLSL bits
that were in src/mesa/shader/

2. Move src/mesa/shader/slang/ to src/mesa/slang/ to reduce the tree depth

3. Rename src/mesa/shader/ to src/mesa/program/ since all the
remaining files are concerned with GPU programs.

4. Misc code refactoring.  In particular, I got rid of most of the
GLSL-related ctx->Driver hook functions.  None of the drivers used
them.

Conflicts:
	src/mesa/drivers/dri/i965/brw_context.c