[Mesa-dev] i965 vertex shader texturing support

[Kenneth Graunke]

This series adds vertex shader texturing support to the i965 driver, as
required by OpenGL 3.0.  Only two things remain: textureGrad() on shadow
samplers (which isn't supported in hardware), and coordinate clamping to
support proper filtering at texture borders.

While I added code for texturing on all generations, I'm only enabling it
on Gen6-7 for now due to lack of testing: my texelFetch and textureSize
tests fail to run on Gen4-5 due to unrelated interpolation bugs.

Thanks in advance for the review!