NFS has no problems with lingering references to unlinked directory
inodes.

CC: Trond Myklebust <Trond.Myklebust@netapp.com>
CC: linux-nfs@vger.kernel.org
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>