NFS made dev_t-agnostic.  Aside of minor fixes in debugging printks,
and adding old_encode_dev()/old_decode_dev(), the main part is in handling
of exports with large dev_t.  New fhandle format introduced, fh_verify(),
fh_compose() and exports cache taught to deal with it.  Format is used when
->s_dev of exported fs doesn't fit into 256:256; in that case we put major
and minor in separate words in fhandle; ->fh_fsid_type is set to 2.