When Robert Redford went to Cuba in 1988, he was interrogated by U.S. Treasury Dept. agents upon his return. After all, he was said to have gone scuba-diving with Fidel Castro. Now the actor is set to fly to Havana on Friday, after his Sundance Film Festival ends, to show his new movie, "The Motorcycle Diaries," to Che Guevara's widow, Aleida March. Redford is an executive producer of Walter Salles' film about Che's consciousness-raising nine-month motorcycle trip through South America as a 23-year-old medical student. The pic got a standing ovation Saturday at a fest screening in Park City, Utah....