Convert sleep_on() to wait_event_timeout().  Probably safe with the BKL but
could be racy once BKL use in NFS-client is gone.
Acked-by: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>