By BOBBY CAINA CALVAN and MARC LEVY (AP) — A man firing a rifle killed shoppers at an Indiana mall’s food court. A gunfight at a Houston home killed four people. A stand-up act by the comedian Craig Robinson in North Carolina didn't even begin before club-goers fled from a man with a gun. In Las Vegas, the specter of gunfire at the MGM Grand sent the crowded casino into pandemonium over a panic that