- the PREEMPT_ACTIVE trick is not needed

- schedule() should check for need_resched, we might miss a
  reschedule otherwise.

the cleanup also fixes the bug. The only reason why i kept
preempt_schedule() was to fix up p->state to TASK_RUNNING,
to make it possible to preempt from places that mark the
task TASK_UNINTERRUPTIBLE before adding the task to a waitqueue,
and thus a preemption in that small window could cause the
task to be removed from the runqueue erroneously.