Factorise SH coefficient in an UBO
Remove extra uniforms in IBL shader
Fix memory leak.
Added support for wip-tracks and wip-karts directories, which are only
used when artist debug mode is enabled.
Remove enet modifications. Fixes #21.

Also stop allocating the address on the heap which was not freed.
Use system enet by default.

Patch by Igor Gnatenko.
Taken from http://pkgs.fedoraproject.org/cgit/supertuxkart.git/tree/0003-unbundle-enet.patch.
Fall back to bundled enet if no system library found.