st/mesa: do vertex and fragment color clamping in shaders
For ARB_color_buffer_float. Most hardware can't do it and st/mesa is the perfect place for a fallback. The exceptions are: - r500 (vertex clamp only) - nv50 (both) - nvc0 (both) - softpipe (both) We also have to take into account that r300 can do CLAMPED vertex colors only, while r600 can do UNCLAMPED vertex colors only. The difference can be expressed with the two new CAPs.