“ Long ago, this Court made clear that no direct appeal lies under § 1253 to the Supreme Court from a temporary restraining order issued by a single judge, even though the order may amount to an 'interlocutory injunction' and may have been issued in an action required to be heard by a three-judge court. ”

“ A court of appeals is not 'powerless * * * to give any guidance when a single judge has erroneously invaded the province of a three-judge court.' Idlewild Bon Voyage Liquor Corp. v. Epstein, supra, at 716, 82 S.Ct., at 1296. Thus, if a single judge oversteps his limited authority under § 2284 (3) , a court of appeals may correct his error. ”