Disabled GIF image file support.
- NOTE: GIF loading is broken since we are forcing freeimage to build and
- load files in big endian mode, while GIFs use little endian.
- This causes gif file headers to be loaded incorrectly, generating
- wrong width/height and crashing the universe.
- If we do not force big endian, on some platforms (like the OpenSUSE
- version used in CAVE2) freeimage will compile with the wrong endianness
- and JPEGS will load with RGB channels inverted. There is probably a
- workaround for all this, but disabling gif loading is a simple solution
- (GIFs can be converted to png)