[quake3] Some Mac usability issues

[Ryan C. Gordon]

> I'd like to avoid OS-specific key combinations for consistency and to
> prevent things like what you mentioned from happening.

There _will_ be people that want Apple-Q to quit the game on Mac OS 
X...I always end up adding an #if MACOSX block that catches that key 
combo to everything I work on...

Other than that, people are usually willing to accept the usual Linuxy 
things (ctrl-g, alt-enter) across platforms.

--ryan.