Ben Affleck made a surprise appearance at Comic-Con in San Diego on Saturday. He joined Superman, a.k.a. actor Henry Cavill, to promote the sequel to “Man of Steel,” which will feature Affleck as moody superhero Batman opposite Cavill and Gal Gadot as Wonder Woman. Affleck and the cast apparently said nothing while onstage, but director Zack Snyder did show some clips of the film, which is still in production. Snyder has been teasing fans with small glimpses of the movie. He tweeted a look at Affleck in his Batman costume on Thursday. . . . Other Boston-area stars at Comic-Con over the weekend included New Hampshire’s Seth Meyers, who promoted his animated series, “The Awesomes,” and Sudbury’s Chris Evans, who joined Robert Downey Jr. and company to promote “Avengers: Age of Ultron,” which is due out next year. While on the Comic-Con carpet, Evans, a.k.a. Captain America, got a hard time from the franchise’s Thor, Chris Hemsworth .