“ On review the Court of Appeals held that it need not decide the 'extremely difficult' factual question of who was negligent because, in the court's view, the barge owner had agreed in the towage contract to assume liability for all losses arising out of the towage, including those caused by the tower's negligence. ”

“ But Southwestern Sugar is not applicable here, for in that case the Court merely preferred to give the Interstate Commerce Commission an opportunity to rule on an exculpatory clause which was part of a tariff filed with the Commission. ”