Use flags to avoid hashing textures when unchanged

If only parameters change (like wrapping or clut, etc.) we don't need to rehash the data - we know it hasn't changed.

Should reduce the distance between lazy texture hashing on and off.

This improves performance mainly in 2D games.  For example Popolocrois is quite happy with this change, as well as Valkyrie Profile.  However, some 3D games benefited from it as well.

-[Unknown]