Homeless Sparked Fire in Bel Air:  Los Angeles investigators have found that the source of the fire that destroyed six homes and damaged a dozen others in the exclusive Bel Air neighborhood was a nearby homeless encampment.   Gale Holland, Laura J. Nelson and David Zahniser of the Los Angeles Times report that the encampment was in a canyon a few hundred feet from the 405 freeway, which was shut down due to the fire during rush hour last Wednesday.  There are an estimated 58,000 homeless living in the Los Angeles area, with many thousands living the West Los Angeles hills, home to some of the most affluent neighborhoods in the country.  "We knew it was only going to be a matter of time before something horrible happened," said one Bel Air resident.  The homeless population Los Angeles has increased dramatically over the past several years.