Kristen Wiig’s character, Maxine, chats brightly at a woman lying comatose in a bed while she rifles through her closet and “borrows” her designer clothes. But Maxine’s chattiness is key to what Abe Sylvia’s adaptation of Juliet McDaniel’s novel, “Mr. and Mrs. American Pie” is trying, albeit unevenly, to pull off. In this instance, it partially exonerates