[Piglit] test KHR_gl_image v2

[Abdiel Janulgue]

This test is a bit more comprehensive and now adds cubemap
support. I've also tried to address the comments.

Let me know if I still overlooked something. :)

The series lives on 
git at gitorious.org:mesa3d/piglit.git cubemap_test branch.

Cheers,
Abdiel
--
 tests/all.tests                                    |    5 +
 tests/spec/CMakeLists.txt                          |    1 +
 .../spec/khr_gl_texture_image/CMakeLists.gles2.txt |   17 +
 tests/spec/khr_gl_texture_image/CMakeLists.txt     |    1 +
 .../khr_gl_texture_image/khr_gl_texture_image.c    |  403 ++++++++++++++++++++
 5 files changed, 427 insertions(+)