Old-fashioned holiday musicals don’t get much more old-fashioned than Irving Berlin’s White Christmas. The David Ives and Paul Blake adaptation of the 1954 film that starred Bing Crosby, Danny Kaye, Rosemary Clooney, and Vera-Ellen runs at Santa Rosa’s 6th Street Playhouse through Dec. 22.  Fans of the film won’t be disappointed as it’s a faithful…