[Mesa-dev] [RFC] softpipe: initial attempt at ARB_viewport_array

[Edward O'Callaghan]

The follow patch passes all but two tests on softpipe for
ARB_viewport_array. Although, admittedly the tests it does
fail are basically the most imported :p. There are a couple
of things needed to polish this off but this gets most of
the fluff out the way I guess. I was unsure how to handle
the generalisation of cliprect unfortunately.