“ Maybe the judge's conduct called for a curtain lecture. At most, that was a matter for the Pennsylvania Supreme Court, and that court did not see even an error of state law in the judge's conduct, let alone a federal constitutional question. We sit only to determine federal constitutional questions, not to scold state trial judges. It is utterly incomprehensible to me how a judge can commit a denial of federal due process by being facetious in the sentencing of defendants where the sentences he imposes are within the limits prescribed by statute. ”