A Manhattan subway train derailed Sunday morning after a maniacal, laughing vandal tossed metal clamps onto the tracks, police sources said. The uptown A train was about 50 feet into the 14th St. station in the West Village when it ran into the metal tie plates, also known as D plates at 8:14 a.m. Three passengers suffered minor injuries. One refused medical attention, another was treated at the scene and the third was taken to Bellevue Hospital for further treatment, officials said. The plates are normally used to secure tracks to the roadbed. Cop sources said the ones thrown onto...