anchor.diff:  
     upstart = pkgs.upstart;
   
  +  userExists = u:
  +    (u == "") || any (uu: uu.name == u) (attrValues config.users.extraUsers);
  +
  +  groupExists = g:
  +    (g == "") || any (gg: gg.name == g) (attrValues config.users.extraGroups);
   
     # From a job description, generate an Upstart job file.
     makeJob = job:
  
positive.code:     # do status queries.
      services.dbus.packages = [ upstart ];
  
    };
  
  }
  
negative.code:         The value <literal>daemon</literal> means that the daemon will
          fork twice.  The value <literal>stop</literal> means that the
          daemon will raise the SIGSTOP signal to indicate readiness.
        '';
      };
  
      setuid = mkOption {
        type = types.string;
        check = userExists;
        default = "";
        description = ''
          Run the daemon as a different user.
        '';
      };
  
      setgid = mkOption {
        type = types.string;
        check = groupExists;
        default = "";
        description = ''
          Run the daemon as a different group.
        '';
      };
  
  