WASHINGTON (AP) - Authorities concerned about terrorism canceled or delayed four flights in 24 hours between London and Washington Dulles International Airport, tightening the security net over U.S. airspace. The flurry of activity over New Year's took place a week and a half after the Bush administration raised the national terrorism alert to orange, its second-highest level. In the face of extreme security at the nation's airports, seaports and public gathering places, no terrorist incidents took place. But the heightened security caused some inconvenience for passengers at Dulles, just outside the nation's capital. Based on security advice from the British...