They could have played it safe, but maybe there’s nothing to lose. With Hollywood coming out of its weakest box-office summer in two decades, the annual fall serious season is loaded with high-stakes gambles and unsure things. It’s as if the entire film industry had decided to lead with its chin and dare audiences to accept the unexpected. If ever a slate of movies had “PROVE IT” stamped on its forehead, this is it. Check out a sampling of what’s coming to theaters this fall, including “The Twilight Saga: Breaking Dawn, Part 2,” “Lincoln,” and “Cloud Atlas.”