Michael Schulman: Kite-Flying with Emma Thompson: The New Yorker In every job that must be done, there is an element of fun. The words belong to Mary Poppins, coaxing the Banks children into tidying their nursery, but they are equally true of film promotion. So it was with Emma Thompson, who was in town recently to talk about her new movie, "Saving Mr. Banks." Thompson plays P. L. Travers, the persnickety author of the "Mary Poppins" books. ("Mary Poppins never explains anything," Travers told this magazine, in 1962. "I don't think explaining helps anything.") Tom Hanks plays Walt Disney, who must persuade her to hand over the book rights for the sake of movie magic. "It took years for Walt Disney to get this character from her," Thompson said. She felt that he was going to make her sweet and sentimental. . . .