Cleanup of derived state calculation prior to seperating software T&L

Cleanup of derived state calculation prior to seperating software T&L
into a new directory.  Specifically the handling of changes to lighting
lighting space (light in model vs. light in eye) have been revamped.

Moved several derived values used only by swrast into that directory.

Removed direct calls to swrast_flush() from vbrender.c -- pushed into
ctx->Driver.RenderFinish.

Optimized flat-shading case in swrast_setup.