IPv6: tunnel over IPv6

I tried to add IPv6 support to tunneldigger, but the server seems to have some problems.
Client seems to work fine. It sends out the exact same bytes as for IPv4.

Perhaps you guys can provide me more information about python with the gevent.socket...
you can simply use this branch to try it by your self.

If IPv6 is working, I'm going to split this PR in handy parts to get this in your master (if you like)

DO NOT MERGE this is currently not working. (broker makes trouble)
I discovered, that you recently added dns name support...so my implementation is duplicated...