Hidden services, minor changes

creating rendezvous is now actually working. 

Some problems I'm still facing:
 - a tunnel that ends in the introduction point itself is needed for the intro1 message, but did not find a way to achieve this. Same holds for rendezvous1 message.
 - the callback functions for sending messages after creating tunnels sometimes require arguments that are not available from the scope of the callback function (e.g. providing an earlier created cookie or service-key as payload in a message that is sent just after creating a tunnel. 
 - Figure out what to to with the check_* functions

Let's have a look at it tomorrow :)