Improve the texture cache hash on x86.

It's a bit less weak now, but still not strong.  Still fairly fast, it
seems like.
Speed up color conversion using SSE.

Probably not the very most optimal implementation, but faster and SSE2.
Make sure clut memory is aligned.

For SSE color conversion, etc.
Cut down on color conversion instructions (x86.)
Correct texcache alignment check.

Oops.
Merge pull request #4386 from unknownbrackets/texcache

Improve the texcache hash (sse only) and sse texcache color conv