BOSTON --Massachusetts Gov. Mitt Romney on Thursday activated the National Guard to help with security at Logan International Airport for the first time since the Sept. 11 terror attacks, after a terror plot targeting U.S.-bound flights was foiled in London. The security alert was raised at Logan and airports around the nation early Thursday after officials in Great Britain disrupted a plan to blow up airplanes from England to the United States. U.S. Homeland Security Secretary Michael Chertoff said the plot appeared to be engineered by al-Qaida, the terrorist group that hijacked two planes from Logan on Sept. 11, 2001,...