By Julian Fellowes (to Eric Estrin)   When Julian Fellowes signed on to write the “Gosford Park” script that later won him an Academy Award, it was actually his second Hollywood breakthrough, his first one coming as an actor some 20 years earlier. He built on his acting success in the U.S. and his native Britain to become a successful producer, director and novelist and also wrote the book for the Broadway musical adaptation of “Mary Poppins.”   Fellowes, ...