Fs_AddToSearchPath now prepends directories to search paths, which allows ~/.quake2world/default to override the pk3 file contents the way it should. Also enable symbolic link following so that users can link in Quake2's .pak files for kicks.
Move shaders into source tree, shaders are now installed to libdir / pkglibdir as part of 'make install'. Also update shaders so that r_draw_wireframe works. This also opens the door for having the old r_draw_lightmaps work with shaders.