Not one from the files, but apparently a brand new case.   An assistant scoutmaster on Long Island has been charged with sexually abusing a 12-year-old boy at Boy Scout retreats and meetings over an 11-month period last year. Jonathan Spohrer, 26, was arrested by Nassau County police at his North Bellmore home on Thursday. He pleaded not guilty on Friday to a charge of second-degree sexual conduct against a child. Spohrer's lawyer, Joseph Carbone Jr., said his client denies t