Don't try to create an IPV6 socket when unecessary

Specifically, if there are no IPV6 nameservers in the configured nameserver list, there's no reason
to open an IPV6 socket.
Merge pull request #24 from rosscooperman/avoid-ipv6-when-uneccessary

Don't try to create an IPV6 socket when unecessary
Will be on release 0.8.3 later this week with other bugfixes/pull requests.