[Piglit] [PATCH] ubo/execution: test {row, column}_major mat4 access

[Florian Will]

> Existing tests apparently never attempt to read data from row_major
> matrices in their UBOs. This catches Mesa bug 104553.

Ilia Mirkin pointed out that
./generated_tests/random_ubo-arb_uniform_buffer_object.py script
generates tests similar to this one en masse, and those tests are much
more thorough than my proposed test. Those tests are not generated
when using the "all.py" test suite though, so I didn't know about
them.

So I think this patch is not really needed.

One minor (or in this special case, major) issue with that script is
that it only checks matrix contents using m[i].{x,y,z,w} and never
uses the m[i][j] syntax (same for vectors). I have modified the script
a bit to generate [j] checks in addition to .{x,y,z,w} checks. If that
seems like a good idea I can send the (quite obvious) patch, but I
think that feature is only supported in OpenGL 3.x+ and the tests
currently support 1.3, so maybe it's better to keep it that way.