Fix unmount when a chroot name is a prefix of another.

E.g. unmounting `precise` will also umount directories under `precisecore`, as grep matches any
mount that starts with `/usr/local/chroots/precise` .
unmount-chroot: Use basic regex instead of extended.
Add backups, restoring, and a spinner to edit-chroot.

Fixes #190.
Merge branch 'master' into croagh