Add tests/spec/glsl-es-1.00/execution/maximums shader tests

Adds gl_MaxCombinedTextureImageUnits.shader_test
     gl_MaxDrawBuffers.shader_test
     gl_MaxFragmentUniformVectors.shader_test
     gl_MaxTextureImageUnits.shader_test
     gl_MaxVaryingVectors.shader_test
     gl_MaxVertexAttribs.shader_test
     gl_MaxVertexTextureImageUnits.shader_test
     gl_MaxVertexUniformVectors.shader_test

These check the built-in constants of the same name from
section 7.4 of the glsl es 1.0.17 spec.

v2: squash patch, address one by one spec reference.

Signed-off-by: Tom Gall <tom.gall@linaro.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
GL_ARB_fragment_program/sparse-samplers: Test for a bug in i965.
glsl-1.40: Add a simple test of math on uniform buffer loads.

Catches an assertion failure/rendering failure in i965.