In Don't Come Knocking, Sam Shepard's aging cowboy star flees the set of his latest movie for the wreckage of his old life. Director Wim Wenders' ambling tribute to American backwaters finds gems by the roadside but eventually drives off the map. EXTRAS In a commentary, Wenders likens Butte, Mont., to the sparse romanticism of Edward Hopper. (A small-town Nevada casino is, by contrast, ''hell.'') The deleted bits he mentions aren't here, but two featurettes take in most of the cast, and Wenders and Saint swap compliments in a brief chat.