PG-13 | 1h 46m | Action, Drama, History | July 21, 2017 “Dunkirk” goes on the same shelf with “Apocalypse Now,” “Platoon,” “Saving Private Ryan,” and “Braveheart.” The only difference is that those four premiere war movies contain brief flashes of levity and even fun, whereas “Dunkirk” is one long, sustained note of grim melancholy. This is not…