TOCTOU race between Quit() and reconnection

[slingamn]

1. We check irc.quit at the start of Connect():

   irc-go/ircevent/irc.go

   Lines 615 to 617 in 5474a63

   	if irc.quit {
   	return ClientHasQuit // check this again in case of Quit() while we were asleep
   	}

2. This check can succeed and then Quit() can be called concurrently with the actual dial call
3. The client will reconnect to the server and renegotiate, but will eventually be disconnected by the serverDidNotQuit check (we will think that we sent QUIT, so we'll wait for the server to disconnect us, but we won't wait forever)

We should probably just check irc.quit again after the dial succeeds, and if so, hang up.