This change allows you to restrict one password to be used with
only one peer. Just add "ipv6" : "ipv6:addr:::::" to your
authorizedPasswords section. After this, only that ipv6 address/
publick key/private key can use that password to connect.

If configuration is not there, password can be used with many
peers, just like before.
Buffix; possible pointer out of scope, as discussed here:
https://github.com/cjdelisle/cjdns/pull/535#discussion_r12781463
Merge branch 'master' of git://github.com/Nite69/cjdns into accidental-public-peers
Better error handling when there is an invalid IPv6 address