Yes, I know busybox is in feature freeze. If this two-liner is too much
that's fine, but it's handy.
This patch allows busybox mount to support "-o move" just like it
supports "-o bind", which is the equivalent of util-linux "mount --move".
Usage is:
mount -o move /mnt/point/1 /mnt/point/2
where /mnt/point/1 is an already mounted filesystem; it will be moved to
/mnt/point/2.