why we shouldn't be slightly stricter here, so I'm just going to
   keep sending this until I'm told to stop.... Make sure that
   unmapped errors are approximately in the range of defined NFS4
   errors.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <trond.myklebust@fys.uio.no>