Update the userland scheduler. Fix scheduler interactions which were

Update the userland scheduler.  Fix scheduler interactions which were
previously resulting in the wrong process sometimes getting a full 1/10
second slice, which under heavy load resulted in serious glitching.
Introduce a new dynamic 'p_interactive' heuristic and allow it to effect
priority +/- by a few nice levels.

With this patch batch operations such as buildworlds, setiathome should not
interfere with X / interactive operations as much as they did before.

Note that we are talking about the the userland scheduler here, not the
LWKT scheduler.  Also note that the userland scheduler needs a complete
rewrite.