Just when you thought Diane Keaton had starred with every Hollywood leading man, along comes news that she will next star opposite Robert DeNiro in ‘Gentle Down the Stream’ about a divorced couple who pretend to be married again for the sake of their adopted son’s happiness on his wedding day. Keaton’s long list of leading men includes Richard Gere, Al Pacino, Warren Beatty, Steve Martin, Jack Nicholson, Harrison Ford, Keanu Reeves and Sam Shepard. Keaton and DeNiro did appear together in Marvin’s Room but not as a couple. Also signed on are Katherine Heigl and Amanda Seyfried. Saw Diane at a press junket months back and she’s still got it.