Matarese v. LeFevre

recognizing the power to raise plain error sua sponte | "Congress intended ... rule [17(b) ] serve as a means of implementing the Sixth Amendment right to compulsory process." | court erred in refusing to sequester witness after testimony, because rule applies prospectively and retrospectively, to preclude witnesses who have already testified from discussing the case with the other witnesses | failure to specify the order or decision was not a jurisdictional defect