“ A person who, as a witness before a special examiner, refused to produce books and papers on the ground that to compel him to do so would invade his constitutional rights, was proceeded against for contempt, and the authority of this court to directly review the final judgment committing for contempt was rested upon the express ground that the writ of error directly involved the determination of whether the order to produce, and to punish for the refusal to produce, violated the constitutional rights of the witnesses. ”