pt-kill --execute-command creates zombies

Children are not waited for, so they become zombies:

3726 if ( $o->get('execute-command') ) {
3727 exec_cmd($o->get('execute-command'));
3728 msg('Executed ' . $o->get('execute-command'));
3729 }

And

3785 # Forks and detaches from parent to execute the given command;
3786 # does not block parent.
3787 sub exec_cmd {
3788 my ( $cmd ) = @_;
3789 PTDEBUG && _d('exec cmd:', $cmd);
3790 return unless $cmd;
3791
3792 my $pid = fork();
3793 if ( $pid ) {
3794 # parent
3795 PTDEBUG && _d('child pid:', $pid);
3796 return $pid;
3797 }
3798
3799 # child
3800 POSIX::setsid() or die "Cannot start a new session: $OS_ERROR";
3801 my $retval = system($cmd);
3802 $retval = $retval >> 8;
3803 PTDEBUG && _d('child exit status:', $retval);
3804 exit $retval;
3805 }

We need a waitpid() to reap the child processes that have terminated. The workaround is to stop and restart the entire process.