When the command completes, make the monitor the foreground process

When the command completes, make the monitor the foreground process
group before informing the main sudo process of the command's exit
status.  This will prevent processes started by the command (which
runs in a different process group) from receiving SIGHUP since the
kernel sends SIGHUP to the foreground process group associated with
the terminal session.  The monitor has a SIGHUP handler installed
so the signal is effectively ignored.