Worlds are colliding, my friends, as George Costanza would say. No, Clooney hasn’t joined the “Downton Abbey” cast (but how much fun would that be? Perhaps he could play a handsome bounder named, oh, Lord Silverhair of Bigglesworth-upon-Tweed, or something), but he’s dropped by to promote a British holiday charity. Perhaps he’ll stay for a dinner party or two. We can hope.