helo: added IPv6 support to invalid_localhost

and also suppress a test warning
A colleague of mine expressed the "ipv4 or ipv6 localhost" check like this:

$self->connection->remote_ip =~ /^127\.|:127\.|^::1$/

I'm honestly not quite sure what's with the /:127\./ bit.  But I'm trying to find out in case it amounts to a useful suggestion ;P