KNOWN BUGS
- Runs on OSX, but doesn't support the mac version of xscreensaver and 
therefore can't be used as a screensaver.
- The --limit option doesn't work exactly as described. It only really
works on really fast setups where it would otherwise run at >300fps.
But thats all it really needs to do.
- add-user-entry.sh contanis a $(cmd) style subshell invocation, that
is incompatible with very old versions of sh. See comment in script.
