Add hfrag, clean up some background renderer stuff

[water111]

This adds hfrag, but with a few remaining issues:

• The textures aren't animated. Instead, it just uses one texture.
• The texture filtering isn't as good as at it could be.

I also cleaned up a few issues with the background renderers:

• Cleaned up some stuff that is common to hfrag, tie, tfrag, shrub
• Moved time-of-day color packing stuff to FR3 creation, rather than at level load. This appears to reduce the frame time spikes when a level is first drawn by about 5 or 6 ms in big levels.
• Cleaned up the x86 specific stuff used in time of day. Now there's only one place where we have an ifdef, rather than spreading it all over the rendering code.