Ridley Scott, director of “Alien” and “Blade Runner,” has signed on to turn a British TV crime trilogy, “Red Riding,” into a Hollywood movie. The trilogy mixes fact and fiction against a background of  child murders and police corruption in the early Thatcher years. Historian David Thomson caused a stir at the Telluride Film Festival in Colorado over the Labor Day weekend when he called the trilogy “Better than ‘The Godfather.’ ” Just how it will fare under Scott is anybody guess.