WASHINGTON - The government is getting ready to test a new risk-detection system that would check background information and assign a threat level to everyone who buys a ticket for a commercial airline flight. The system, ordered by Congress after the terrorist attacks of Sept. 11, 2001, will gather much more information on passengers than at present. Delta Air Lines will try it out at three airports beginning next month, and a comprehensive system could be in place by the end of the year. Transportation officials say a contractor will be chosen soon to build the nationwide computer system, which...