Small optimization to typical 4-bit textures.

These aren't used that often, but this makes them a bit faster.

It also looks cleaner, imho.
Cache cluts by hash not address.

This makes it immensely faster in Final Fantasy Tactics, and fixes the
numerous graphical issues.
Get rid of the cluthash in the texcache.

It's part of the key now, and better anyway.
Merge pull request #1568 from unknownbrackets/texcache

Hash cluts rather than using the address