Rasterizer core only supports polygonmode front==back.  Add logic for
populating fillMode for the rasterizer only for that case correctly.
Provide enum conversion between mesa enums and core enums.

The core renders lines/points as tris. Previously, code would enable
stipple for polygonmode != FILL.  Modify stipple enable logic so that
this works correctly.

No regressions in vtk tests.
Fixes the following piglit tests:
	pointsprite
	gl-1.0-edgeflag-const

v2: remove cc stable, and remove "not implemented" assert
v3: modified commit message

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>