Agence France-Presse: British oil giant BP used robotic underwater vehicles Sunday to try to cap a leaking well and prevent a growing oil slick in the Gulf of Mexico from developing into an environmental disaster. Satellite images showed the slick had spread by 50 percent in a day to cover an area of 600 square miles (1,550 square kilometers), although officials said some 97 percent of the pollution was just a thin veneer on the sea’s surface. BP has dispatched skimming vessels to mop up the oil …