Patch for login exchange timeout

[Damien Miller]

Mic Bowman wrote:
> Here's a quick patch that adds a timeout (value set
> from the connection timeout config parameter) for
> identification exchange. 

I think the idea is ok, but IMO the implementation should do
select+timeout rather than use signals.

Also, maybe the timeout for the banner exchange should be
ConnectionTimeout less the time actually used during the connect phase.

-d