Patch by Alfredo de Greef with high quality image texture filters.
This adds 3 new filters:
* SAT: Summed Area Tables. This is like mipmaps, but using somewhat
more memory avoids some artifacts.
* EWA: Ellipitical Weighted Average, anisotropic filter.
* FELINE: Fast elliptical lines for anisotropic texture mapping.
The one change I made to this was to try to fix an alpha/premul
problem, hopefully I didn't break anything, it looks compatible
with the existing filter now for me.
e3c6ae9b89