There were plenty of real-life heroes on hand Saturday night at the Tribeca Film Festival’s closing screening of “The Avengers,” with emergency first-responders and members of the military among the crowd that took in the comicbook tentpole.So what do the movie’s thesps consider their real life superpowers? Mark Ruffalo cited his tirelessness and indefatigability, particularly in his work to stop fracking in upstate New York, a campaign that’s been an important cause for him for a few years now. Chris Hemsworth went all aw-shucks when asked, but eventually fessed up to being a committed and passionate guy. Clark Gregg, on the other hand, didn’t skip a beat. “I have a ridiculous gift for finding a parking spot,” he said. Last-nighters took the party to House of Imagination.