#75 tilesort does not support ActiveTextureARB

[Chris Greenhalgh]

(I think) Due to a combination of:

- making ActiveTextureARB and TexEnv* NOPs

- state_tracker/state_texture.c not marking texture state
as dirty on ActiveTextureARB

- also small omission from state_tracker/state_texdiff.c
which does not check that correct texture unit is current
if only environment is dirty

alternative versions of state_tracker/state_texture.c and
spu/tilesort/diffapi.py attached.
state_tracker/state_texdiff.c also includes fixes/changes
mentioned in the bug report about not propagating
texture lod MAX_LEVEL.

[Chris Greenhalgh]

tar of files with fixes