Patch fixes Piglit test: arb_gpu_shader_fp64/preprocessor/fs-output-double.frag and adds additional validation for shader outputs. Signed-off-by: Tapani Pälli <tapani.palli@intel.com> Signed-off-by: Dave Airlie <airlied@redhat.com> Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>