BERLIN ? German authorities shut down and cleared thousands of fans from a popular rock music festival Friday night after receiving a "concrete" terrorist threat.Rhineland-Palatinate government spokesman Joachim Winkler told the dpa news agency that there were tips of a possible terrorist attack and that the Rock am Ring festival was shut down on its opening night as a precaution.The German band Rammstein was the Friday night headliner, but hadn't yet started playing.Organizer Marek Lieberberg told journalists at the scene that he hoped the annual...