function validate_working(MessageSet $ms = null)
 {
     $status = RepositorySite::run_ls_remote($this->ssh_url(), $output);
     $answer = join("\n", $output);
     if ($status == 0 && $ms) {
         $ms->set_error_html("working", Messages::$main->expand_html("repo_unreadable", $this->message_defs($ms->user)));
     }
     if ($status > 0 && !preg_match(',^[0-9a-f]{40}\\s+refs/heads/master,m', $answer)) {
         if ($ms) {
             $ms->set_error_html("working", Messages::$main->expand_html("repo_nomaster", $this->message_defs($ms->user)));
         }
         $status = 0;
     }
     return $status;
 }