BERLIN -- American filmmaker Laura Poitras, known for her award-winning 2014 documentary on former U.S. intelligence contractor Edward Snowden and his revelations about the National Security Agency, has once again turned her camera on the watchmen.In an exhibition opening Friday in Berlin, Poitras examines the way the state monitors citizens' lives — both abroad and at home, in New York City.While her early work on the war in Iraq and the U.S.