The Smollett quotation above predates Twain by some time. I'm not sure if the Smollett quotation is the earliest recorded reference to the phrase, but it's the earliest I've found. Smollett was Scottish, which may give a nudge towards the hanging rogue theory, however, he also served as a surgeon in the Royal Navy, so must have witnessed many floggings, as well as treating the victims. Take your pick.