“A non-exclusive jurisdiction agreement precludes either party from later arguing that the forum identified is not an appropriate forum on grounds foreseeable at the time of the agreement, for the parties must be taken to have been aware of such matters at the time of the agreement. For that reason an application to stay on forum non conveniens grounds an action brought in England pursuant to an English non-exclusive jurisdiction clause will ordinarily fail unless the factors relied upon were unforeseeable at the time of the agreement.”