Patches into CVS

[Brendan Burns]

Hey folks,
the two recently discussed patches have been added into CVS and the
makefile has been modified so if you set BUILD_ARTS to YES it will build
and use snd_arts.c instead of snd_linux.c for the straight up linux
binary.  The SDL binary still uses snd_sdl.c (that kind of makes sense
huh ;-)

Also the gamma adjustment patch has been added.  Update to your hearts
content.

--brendan