This adds a simple test which sets an alpha test on a pipeline and
then renders a texture. It then verifies that the transparent parts of
the texture aren't drawn. This is currently failing with the GL3
driver because GL3 requires the alpha test to be implemented in GLSL
but the generated alpha test uniform is only updated for the GLES2
driver.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit 4ec04507bfaf2d61707dccfb59ac7326962ee741)
