There is an extended sequence some way into 12 Years a Slave that is so beautifully composed and executed, its subject so cruel and true, the effect both extreme and oddly quotidian, that it is a small film in itself. In the lush greenery of an antebellum estate, the mansion itself visible to one side, a man dangles, strung up from a tree, his toes just feeling for purchase on the ground. As he shifts to reduce the pressure of the rope – struggling to breathe but all too conscious – other slaves emerge from their shacks and slowly, timidly, go about their tasks, barely daring to glance sideways at their fellow’s plight.If this segment of Steve McQueen’s new film were exhibited in a gallery (like the former Turner Prize-winner’s early work) then it would be sh