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>
i965 Gen4/5: Generalize SF flatshading for GLSL1.3

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965 Gen4/5: correctly handle flat shaded attributes in clipper
i965 Gen4/5: clip: Add support for noperspective
dont mangle flatshaded attributes in clipper
i965: allow 8 user clip planes on CTG+