Use update_mtab() to update /etc/mtab on fake mounts (mount -f), else we get
dup entries in /etc/mtab.

Patch by Mike Frysinger <vapier@gentoo.org>

--- util-linux-2.12q/mount/mount.c	2005-09-14 15:37:43.000000000 +0200
+++ util-linux-2.12q.az/mount/mount.c	2005-09-14 15:27:14.000000000 +0200
@@ -662,7 +662,7 @@ update_mtab_entry(const char *spec, cons
 		print_one (&mnt);
 
 	if (!nomtab && mtab_is_writable()) {
-		if (flags & MS_REMOUNT)
+		if (fake || (flags & MS_REMOUNT))
 			update_mtab (mnt.mnt_dir, &mnt);
 		else {
 			mntFILE *mfp;