mesa/uniforms: fix get_uniform for doubles (v2)

mesa/uniforms: fix get_uniform for doubles (v2)

The initial glGetUniformdv support didn't cover all the
casting cases that are apparantly legal, and cts seems to
test for them.

I've updated the piglit test to cover these cases now.

v2: fix indentation - it's all broken in this file (Ilia)
fix src/dst index tracking in light of fp64 support (Ilia)

cc: "11.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Dave Airlie <airlied@redhat.com>