The Mumford-in-Chief and his spectacularly mature-looking sons get to choose who they work with now, so who do they go to first? A fellow folk-hero, similarly suspendered and Civil War-era bedecked? No, you’re thinking too small. It turns out his Mumfordness has been working on some new music with he of suit-and-tie fame, Justin Timberlake. “Marcus and myself, we all kind of worked on the music together,” Justin said. “And I don’t know any other world where we would have the opportunity to collaborate like that, but it was so much fun.” The collaboration in question is for Inside Llewelyn Davis, the new film from the Cohen brothers, so there’s a little something for everyone here …