Test mixing of GLSL versions between VS and GS.

This introduces a new test: "shaders/version-mixing vs-gs", which is
known to fail with Mesa revision 81b998c.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Check that uniform block link errors are detected when skipping stages.

In Mesa, as of commit f38ac41, uniform blocks are only validated
between adjacent shader stages.  That means that if a program contains
vertex, geometry, and fragment shader stages, and the vertex and
fragment shader stages refer to a uniform block that isn't referred to
by the geometry stage, then some linker checks may not be performed.

Most possible link errors get detected at a later stage of linking,
but I found one case that wasn't; this test exercises that case.

Test is known to fail with Mesa f38ac41.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Revert "framework: Add support for a test timeout"

This reverts commit ab2eb660925e3680e868c5f469a4ef32e6dd9a59.
!UPSTREAM: mysteriously failing test