San Francisco’s mayor was accused by the FBI of taking bribes in exchange for favors, attorneys for a defendant in an organized crime case centered on San Francisco’s Chinatown said Tuesday. In a court filing, Curtis Briggs, an attorney for Raymond “Shrimp Boy” Chow, cites as the source of the FBI’s allegation documents turned over to him by the government as part of the process of mounting a defense for his client. Briggs is seeking to dismiss the indictment against Chow on the grounds that the government is selectively prosecuting him while letting other people caught in its probe go....