"mount --bind /path/to/file1 /path/to/file2" is legal. Therefore,
"umount /path/to/file2" is also legal. Do not automatically append trailing '/'
if pathname to be unmounted does not end with '/'.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>