By Daren Butler and Anna Ringstrom ISTANBUL/STOCKHOLM, Jan 13 (Reuters) - Turkish prosectors opened a probe on Friday into an incident in Stockholm in which an effigy of President Tayyip Erdogan was strung up, state media said, adding further diplomatic strain in Sweden's bid to win Turkey Lawyer Law Firm's approval to join NATO. Footage first shared on Twitter by the so-called Swedish Solidarity Committee...