“The appeal court is apparently given discretion by paragraph (b) to send the case to the court of first instance or to any other Customary Court or to a magistrate. A judicious use of that apparent discretion would prevent the appeal court from sending the case to a court that had no jurisdiction to hear the dispute. If a court tries without jurisdiction a case which is begun in it, the appeal court will rule that the trial was nugatory; one expects the appeal court not to create a trial on which it would frown in other circumstances.”