ULE nice behavior fixed.

[Jeff Roberson]

It probably still needs some tweaking but it seems to be MUCH better now.
New algorithm entirely.

nice +20 processes will not run if anything else wants to.

idleprio is still not working correctly.  bde reports that this causes a
3% perf degradation for buildworld.

I'd appreciate feedback from anyone brave enough to try it.  I think my
fork/exit code is still wrong and my cpu estimator is still a bit slow.
I'll work on this soon.

Cheers,
Jeff