"In Thomas's view, no prior litigation involving Alabama's use of the restraining bar would have put a reasonable prison guard on notice that the mere act of attaching a prisoner to it would violate the Eighth Amendment.The three federal district courts in Alabama had all rejected this contention, as well as the idea endorsed by the majority—that exposure to the elements resulting from an extended stay on the hitching post, coupled with the pain caused by the handcuffed—was the wanton and unnecessary infliction of pain.