Removed knowledge of swrast Clear/Bitmap/Accum/Draw/Read/CopyPixels

Removed knowledge of swrast Clear/Bitmap/Accum/Draw/Read/CopyPixels
functions from core mesa -- if drivers need these fallbacks they
must now call them themselves.

Introduced hooks for clip-vertex-interpolation and the rendering
of clipped lines and polygons.  Allows drivers to interpolate
their hardware-format vertices directly.  Used in dri drivers to
replace fastpath code.

Slight optimizations to pipeline build/run routines.