st/nine: Print warnings for r500 when shader is likely to go wrong

st/nine: Print warnings for r500 when shader is likely to go wrong

r500 hasn't enough float constants for vs to fill all needs.
Overlapping issues can happen with complex shaders.
The fix would be to recompile shaders to include the integer
and boolean constants, instead of reserving slots for them.

Reviewed-by: Tiziano Bacocco <tizbac2@gmail.com>
Signed-off-by: Axel Davy <axel.davy@ens.fr>