MOSCOW (Reuters) - Russian President Vladimir Putin and U.S. President Donald Trump greeted each other at an APEC summit in Vietnam, shook hands and exchanged a few words, Russian news agencies reported on Friday. Trump approached Putin at a photo session of world leaders in the Vietnamese city of Danang and gave him a friendly slap on the shoulder, agencies reported. Kremlin spokesman Dmitry Peskov was cited by the RIA news agency as saying that the two men had not held any talks yet however, something Moscow has been trying to set up for days.       