Improve integer texture support & add i965 texture_rgb10_a2ui support

v3:
 * 4 reviewed patches from v2 were committed, and thus removed from
   the series
 * Updated _mesa_meta_CopyTexSubImage to fix an issue with a texture
   using MESA_FORMAT_R8
 * Note: patches 1-3 & 8 of this series have been previously reviewed

v2:
 * Add glformats.c/glformats.h
 * Move integer texture clamping fixes from ReadPixels to CopyTexSubImage
 * updated docs/GL3.txt for i965 & texture_rgb10_a2ui
 * Fix ugly pseudo-template in .h. I just duplicated the code and dropped
   pack_int_cases_tmp.h.

v1:
 * Improve integer texture support
 * Add i965 texture_rgb10_a2ui support