A riot nearly broke out at San Francisco's Civic Center on Friday after the organizer of a giveaway reneged on his promise to hand out $10 bills to the homeless. More than 500 people -- some who had arrived before noon -- showed up for the 4 p.m. giveaway but walked away empty-handed. Joe Canada, an artist from Novato, spoke to the crowd for about an hour but drove away before he or any of his 20 volunteers could hand out any bills. The size of the crowd might have intimidated him, police said. "There were too many people,"...