Solve another handshake problem, where one threads was calling del_event
while cleaning up after receiving a zero byte on the connect socket
(localyy started connection), while another was trying to accept a
new connection from the same peer. Create a zero-timed event and
delocalize the accept into a timer_event.
Add support for registering an error callback, that can be used when a
connection is discovered as failed during the initialization process.
Don't over-do it!