Dan Rather has grabbed some interesting, out-of-the-mainstream music interviews this season – Robbie Robertson, Debbie Harry – all of whom have some quite fascinating stories to tell. Tonight’s guest is Ian Anderson, the lead singer and flute player of Jethro Tull. I don’t know whether he’s going to flout his unusual rock-star past, but, then again, he is a flautist. And I saw Jethro Tull in concert once, when a super-inebriated Anderson vomited in mid-son