By Denny Dyroff, Entertainment Editor, The Times Trolls at the Philadelphia Zoo The Philadelphia Zoo has been a habitat for an amazing array of animals ever since its opening day in July 1874. Now, for the next two-and-one-half months, the Zoo will be home to a sextet of Trolls. Now through April 15, the Philadelphia Zoo (3400 West Girard Avenue, Philadelphia) is hosting the East Coast debut of...