Pixar Animation remains undefeated at the box-office races. The Disney unit's animated sequel "Cars 2" cruised to a No. 1 finish with a $68 million opening weekend, according to studio estimates Sunday. That makes 12 wins in a row for Pixar since the company's first feature film, 1995's "Toy Story." "It couldn't be any better than that. What an unbelievable track record these guys have," said Chuck Viane, head of distribution for Disney. "Cars 2" added $42.9 million in 18 overseas markets,...