This means that a tex_t object is passed in instead of just raw bytes
and width and height, but it means the texture can specify whether it's
flipped or uses BGR instead of RGB. This fixes the upside down
screenshots for vulkan.
This is for the conversion /to/ paletted textures. The conversion is
necessary for csqc support. In the process, the conversion has been sped up
by implementing a color cache for the conversion process. I haven't
measured the difference yet, but Mr Fixit does seem to load much faster for
the sw renderer than it did before the change (many months old memory).
This makes tex_t more generally useable and probably more portable. The
goal was to be able to use tex_t with data that is in a separate chunk
of memory.
