to send, we don't need to check if the connection is still alive.
Furthermore, if we receive any kind of data from the other end, we know
it's alive, so we don't need to check it either. So, PING requests are
only sent if we send packets but there is no response.
furthermore this version does NOT work yet because of a problem with
sending keys (these should be converted to base36 or something like that).
It is possible to telnet to the tinc daemon now and type some commands
by hand though :).
