thread stage 10: (note stage 9 was the kern/lwkt_rwlock commit). Cleanup

thread stage 10: (note stage 9 was the kern/lwkt_rwlock commit).  Cleanup
thread and process creation functions.  Check the spl against ipending in
cpu_lwkt_restore (so the idle loop does not lockup the machine).  Remove
the old VM object kstack allocation and freeing code.  Leave newly created
processes in a stopped state to fix wakeup/fork_handler races.  Normalize
the lwkt_init_*() functions.

Add a sysctl debug.untimely_switch which will cause the last crit_exit()
to yield, which causes a task switch to occur in wakeup() and catches a
lot of 4.x-isms that can be found and fixed on UP.