Moved image and font functionality to rd-common.
Moved tr_noise to rd-common, and improved image loading functinality.
Reformatted code and fixed some bugs.
Clear all image loaders on initialization, and then add new ones.
Removed exe_header.h inclusions from rd-vanilla cpp files.
Corrected 64-bit problem with ghoul2 code.
Added some documentation to some functions in tr_image_load.cpp.
Fixed compilation problem on OSX, and correct iterator usage when erasing
and deleting models.