Cambridge-bred actor Matt Damon took time out of his busy schedule — the Hollywood homeboy is currently filming a sci-fi flick, “Interstellar,” with director Christopher Nolan — to help education historian and activistDiane Ravitch promote her much-discussed new book, “Reign of Error: The Hoax of the Privatization Movement and the Danger to America’s Public Schools.” Damon, whose mom, Nancy Carlsson-Paige, taught a few generations of teachers while a professor at Lesley University, introduced Ravitch to a crowd of students and teachers at California State University Northridge. . . . Closer to home, Luxe Boutique owner Cecil Elrod hosted a fashion show at the Taj Hotel featuring leather, cashmere, and, yes, fur coats. Boldfacers on the runway included Bill Belichick’s significant