Jack LaLanne, the fitness guru who inspired television viewers to trim down, eat well and pump iron for decades before diet and exercise became a national obsession, died Sunday. He was 96.  LaLanne died of respiratory failure due to pneumonia Sunday afternoon.  When he turned 43 in 1957, he performed more than 1,000 push-ups in 23 minutes on the "You Asked For It" television show. At 60, he swam from Alcatraz Island to Fisherman's Wharf in San Francisco — handcuffed, shackled and towing a boat.