This is just copying most of gossipd/gossip.c into connectd/connect.c.
It shares the same wire format as gossipd during transition, and changes
are deliberately minimal.
It also has an additional message 'connect_reconnected' which it sends
to the master daemon to tell it to kill a peer; gossipd relied on
closing the gossipfd to do this, but connectd doesn't maintain an fd
with remote peers.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
