B O S T O N, July 28, 2004 — As Sens. John Kerry and John Edwards arrived in Boston today for the Democratic National Convention, so did the California man who is their single biggest contributor. He is Stephen Bing, a wealthy film producer who, with little fanfare, has managed to steer a total of more than $16 million of his money to Democratic candidates and the supposedly independent groups that support them. "To most of the people who track money and politics, they're like, who the hell is Steve Bing?" said Chuck Lewis, founder of the Center for...