[Piglit] Reworked textureSize and texelFetch tests

[Kenneth Graunke]

I've reworked the tests quite a bit, adding new common.[ch] files for
code useful in both tests (and hopefully more new tests in the future).
While the line count didn't go down, I feel that the tests are a lot
simpler now.  A lot of close-but-not-quite copies of code are gone now.

Other fixes:
- Require GL 3.0 for depth cube maps
- Require GL_EXT_texture_integer for integer formats
- Require GL_EXT_texture_array for array samplers.
- Preliminary framework for sampler2DRect and samplerCubeArray.
- In texelFetch, actually mark the test as FAIL if probes are wrong.
- In textureSize, use proper integer internal formats.
- Use asprintf instead of fixed size buffers (thanks Jose!)

Also, I added support for GL_EXT_texture_swizzle to the texelFetch test.

Feedback welcome.  Ideally I'd like to push these this week.