Ensure setuid bit is restored when the owner changes

 https://bugzilla.redhat.com/show_bug.cgi?id=467936#c7

Cry immediately if we are not running as root.

	$ require_root

	$ touch passwd

	$ chmod 755 passwd

	$ chmod u+s passwd

	$ getfacl passwd > passwd.acl

	$ cat passwd.acl

	> # file: passwd

	> # owner: root

	> # group: root

	> # flags: s--

	> user::rwx

	> group::r-x

	> other::r-x

	>

	$ chown bin passwd

	$ chmod u+s passwd

	$ setfacl --restore passwd.acl

	$ ls -dl passwd | awk '{print $1 " " $3 " " $4}' | sed 's/\\.//g'

	> -rwsr-xr-x root root

	$ rm passwd passwd.acl