[Mesa-dev] Partially finishing GL_EXT_texture_integer.

[Eric Anholt]

The pixel pack stuff is a bit of a WIP.  I think it could probably be
reused for the float pixel pack, with just a bit more massaging.

Remaining known problems with GL_EXT_texture_integer:
- meta copytexsubimage on integer fails.
- mipmap gen fails
- possible filtering occuring on i965 when it shouldn't?
- clamping in pixel pack doesn't happen.
- error return failures from DrawPixels
- error return failures from GetTexImage
- error return failures from ReadPixels
- error return failures from TexImage