Fix P_WSLEEP handling when continuing SSTOP-ed processes

Fix P_WSLEEP handling when continuing SSTOP-ed processes

When continuing a process on the sleep queue just let it switch to
p_stat = SSLEEP even when P_WSLEEP is set. Once a proc is SSTOP-ed
in sleep_finish() a valid sleep point has been reached and there is
no need to make the process runnable again (which results in some
hairy race conditions). Instead simply clear P_WSLEEP since a stopped
proc reached the sleep state and there is no race with wakeup() anymore.

OK mpi@