undo my latest addition: its already covered by "Fallback directory mirrors on IPv6 (0.2.8.0-alpha-dev)" sorry ([diff](https://trac.torproject.org/projects/tor/wiki/org/roadmaps/Tor/IPv6?action=diff&version=32)) URL: https://trac.torproject.org/projects/tor/wiki/org/roadmaps/Tor/IPv6?version=32