Improve CLUT load performance, tweak hashing

Loading the clut was expensive in some games, which were doing it in a row without any flush between (e.g. Disgaea 2.)  This makes that do less work, and simplifies the hash used (still works okay in the games that needed a more complex hash before.)

This also changes MiniHash slightly, so that it can still use the secondary cache.  Before it would fail and reload if the MiniHash failed.

I tried to change MiniHash to a sampling hash (tried ~127 samples), and use that in the cachekey for clut'd textures.  But that unfortunately did not help FF2 (which spends tons of time in SetTexture and friends due to animating the texture data.)

-[Unknown]