On Linux (maybe all unices) Ruby seems to have a
problem with pthreads. After the script ends Ruby hangs
in it's clean up code. No more information is available yet.
- Avoid anything that touches pthreads. Timers and
sound are to be avoided.
- Compile SDL without phtreads. At least sound is
disabled then, maybe more.
- Debug it all and find out what the problem is.