[dx73b] Try2: Performance of texture states

[Ann and Jason Edmeades]

(Try#2 - Also fixes Operation Flashpoint problem which was introduced)

This is the first patch which looks at the performance of changing the
textures on a texture unit. As was pointed out to me by Lucho, certain
information is per texture unit and hence not affected when a different
texture object is bound. This patch on my machine changes the displayed
fps by the Billboard sample from 30.6 to about 42.6. [Actually it was
43.0
with patch b, but I dont see why!]

There is still more optimization which can be done here, but this is a
start.

Let me know if anyone notices any regressions with this one.

Changelog
Only reapply the texture states necessary when a different texture gets
bound to the same texture unit.
Jason