This is a more complicated test with one tinc daemon using a tap interface
(therefore requiring root), and a second one using a multicast interface. A
separate program "pong" is listening on the same multicast address, and waits
for ARP and ICMP packets, responding to ICMP echo packets with replies.
This test doesn't require any configuration of the tap interface.
It now defers reading from stdin until after the authentication phase is
completed. Furthermore, it supports the -q, -r, -w options similar to those of
Jürgen Nickelsen's socket.
