GH-110: entirely new horrors for auto reconnect

Allow connection_fatal to trigger a reconnect attempt, which, if there is
still an issue, which eventually call connection_fatal.  This causes us to
retry indefinitely.  Maybe eventually we'll need to limit this somehow
(exponential backoff?).

Also:
 * Remove wakeup reconnect delay.  Infinite reconnects will fix this itself.
 * Make a dns error a normal connection_fatal.  Oh dear, oh dear.  This was
     hardcoded to just messagebox and outright exit(0);.  Now we keep
     going for a tiny bit, so that we can run the normal cleanup code.
     This is the tiny cleanups to ssh.c.