NASA gave the green light Monday night for a Fourth of July shuttle liftoff despite worries about a piece of foam that popped off Discovery's external fuel tank while the spacecraft sat on the launch pad. The decision was sure to stir more debate about whether the space agency was putting its flight schedule ahead of safety. The 3-inch triangular piece of foam that appeared to come from a 5- inch-long crack late Sunday or early Monday is far smaller than the foam chunk that brought down Columbia, killing seven astronauts in But NASA managers spent most of Monday...