enable front colors if back colors are written
i965 gen4/5: Simplify the bfc copy in the sf

Signed-off-by: Olivier Galibert <galibert at pobox.com>
[V1] Reviewed-by: Eric Anholt <eric@anholt.net>

V2 (Chris Forbes):
Update to use VARYING_SLOT_* rather than VERT_RESULT etc.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965 Gen4/5: Compute interpolation status for every varying in one
place.

The program keys are updated accordingly, but the values are not used
yet.

Signed-off-by: Olivier Galibert <galibert at pobox.com>

V2: Updated for vue_map changes (Chris Forbes)
Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Correctly setup the parameters in the sf
i965 Gen4/5: correctly handle flat shaded attributes in clipper
nopersp
dont mangle flatshaded attributes in clipper
i965: allow 8 user clip planes on CTG+