For their adaptation of William Makepeace Thackeray's 1848 novel Vanity Fair, writer Kate Hamill and director Jessica Stone do a little bit of cheating. Hamill has decided to liven things up by making this a play about a play about a novel. We are in American Conservatory Theater's Geary Theater, but on stage, we're told that our actual location is "Strand Musick Hall," and the opening number tells us that seven actors are going to play all the parts for the next 2 1/2 hours.