fix #2452

We want to call socket() with the parameters provided by getaddrinfo, so we
can’t addd the fd into the poller immediately. We need to wait the
connection attempt, and then the SocketHandler can call add_socket_handler
itself, if the connection succeeds, or is in progress.

fix #2524

Also remove the duplicate send_self_join methods, user only send_user_join

The generated XML is very verbose because each IRC formatting tag makes us
close a <span/> element and reopen it with the new style applied.  However,
this works quite well and is easy to implement.