- Move sched_fork() later in fork() after the various sections of the new

- Move sched_fork() later in fork() after the various sections of the new
  thread and proc have been copied and zeroed from the old thread and
  proc.  Otherwise attempts to modify thread or process data in sched_fork()
  could be undone.
- Don't copy td_{base,}_user_pri from the old thread to the new thread in
  sched_fork_thread() in ULE.  This is already done courtesy the bcopy()
  of the thread copy region.
- Always initialize the real priority (td_priority) of new threads to the
  new thread's base priority (td_base_pri) to avoid bogusly inheriting a
  borrowed priority from the parent thread.

MFC after:	2 weeks