The movie, I’m pleased to report, exerts the same kind of historical/topical force that "13th" did. DuVernay, while she works in an extremely accessible and mainstream way, has a singular gift for making the nuances of history come alive. "14th" is steeped in history, but it’s not a dry lecture. Instead, DuVernay cuts through the dusty complacency with which we tend to regard the Constitution (just hearing that word can make you feel like you’re back in school) and shows you that the Constitutio…