Nearing 60, Madame Streep has become the most bankable movie actress in America. I repeat: the most bankable movie actress in America. The “Mamma Mia!” movie was risibly successful — the only female-driven picture in the Top 50 movies of all time. “The Devil Wears Prada” was also not shabby. And now Streep is about to open in an Oscar-bait movie if ever there was one: “Doubt.” It’s kind of fitting that she plays an imperious nun in this one, because for three decades Streep has ruled movies — not the box-office side but the side made up of anyone who loves good acting. And what has Streep done to cap her annus mirabilis? She’s played another goddess: Julia Child, in the upcoming Nora Ephron flick, “Julie and Julia.” After portraying Child, Streep’s Oscar (and Kate Winslet better hope Academy voters are kind enough to give her the consolation prize of Best Supporting Actress for “The Reader,” because her “Revolutionary Road” performance ain’t going to beat Meryl) will be almost a comedown.