i965: fix bugs in projective texture coordinates

i965: fix bugs in projective texture coordinates

For the TXP instruction we check if the texcoord is really a 4-component
atttibute which requires the divide by W step.  This check involved the
projtex_mask field.  However, the projtex_mask field was being miscalculated
because of some confusion between vertex program outputs and fragment
program inputs.

1. Rework the size_masks calculation so we correctly set bits corresponding
to fragment program input attributes.

2. Rename projtex_mask to proj_attrib_mask since we're interested in more
than just texcoords (generic varying vars too).

3. Simply the indexing of the size_masks and proj_attrib_mask fields.

4. The tracker::active[] array was mis-dimensioned.  Use MAX_PROGRAM_TEMPS
instead of a magic number.

5. Update comments, add new assertions.

With these changes the Lightsmark demo/benchmark renders correctly, until
we eventually hit a GPU lockup...