By Renee Maltezou and Deepa Babington ATHENS (Reuters) - Greece's leftwing Syriza looked set for a comfortable victory over the ruling conservatives, an exit poll showed, with a chance of winning a full majority to face down international creditors and roll back years of painful austerity measures. Syriza could gain 35.5-39.5 percent of the vote, well ahead of the conservative New Democracy ...