Open Sound System

It's already possible to start playing secs into the file; It's handy to also be able to limit the length of playback. Patches attached.

Thanks!

Patches are usually sent to the oss-devel list, but I'll forward a version of this.

As for the patch:
1. I don't think #ifdef is really needed, it's just a small addition.
2. While we're at it, datalimit might as well be a double and accept rational numbers.
3. I tried a slightly different method of implementing this, can you test it?
(it includes some unrelated changes, since datalimit had to be changed all over, fortunately, all the relevant changes ended at the start of the diff).