Replace the flags Mesa was using for ctx->NewState with a new set

Replace the flags Mesa was using for ctx->NewState with a new set
based on the GL attribute groups.

Introduced constants describing the circumstances under which some
key derived values can change:
	_SWRAST_NEW_RASTERMASK -- ctx->RasterMask
	_SWRAST_NEW_TRIANGLE   -- The software rasterizer's triangle
	                          function
	_DD_NEW_FEEDBACK -- the 'DD_FEEDBACK' bit in ctx->TriangleCaps

These are helpful in deciding whether you need to recalculate state if your
recalculation involves reference to a derived value.