Monday, January 19, 2004 By ROBERT STERN Staff Writer PRINCETON BOROUGH - When the U.S. Postal Service launched its "Black Heritage Series" of stamps in 1978 to recognize prominent black people, Paul Robeson Jr. was certain his famous father was bound to make the list. Now, 27 years after the elder Robeson died, the Postal Service will launch a stamp tomorrow in his honor during a ceremony at Princeton University. It's a tribute Robeson admirers say is both well-deserved and long overdue for the trailblazing and sometimes controversial man, whose birthplace and boyhood home at 110 Witherspoon St. is just...