- ftick was initialized to -1 for init and any of it's children. Fix this by

 - ftick was initialized to -1 for init and any of it's children.  Fix this by
   setting ftick = ltick = ticks in schedinit().
 - Update the priority when we are pulled off of the run queue and when we
   are inserted onto the run queue so that it more accurately reflects our
   present status.  This is important for efficient priority propagation
   functioning.
 - Move the frequency test into sched_pctcpu_update() so we don't repeat it
   each time we'd like to call it.
 - Put some temporary work-around code in sched_priority() in case the tick
   mechanism produces a bad priority.  Eventually this should revert to an
   assert again.