We need to track the pid of the connecting control connection to be

We need to track the pid of the connecting control connection to be
able to send answers back to the correct client in case two are
connecting at the same time. We also need to pass the pid around to
the resolver process so that it can hand it back to us.
Debugged by deraadt and dlg who noticed that answers would always
arrive on the first control connection.

deraadt@ points out that tracking the pid is not the best choice in
case one process wants to hold open two connections but at least this
brings us in line with all the other privsep daemons with control
tools. If we change this we should change it in all daemons.