If the automount daemon receives a signal which causes it to sumarily
terminate the autofs4 module leaks dentries.  The same problem exists with
detached mount requests without the warning.

This patch cleans these dentries at umount.
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>