Harper Lee’s sequel to “To Kill a Mockingbird” wasn’t on anyone’s radar until this past year, and arrives a mere 55 years after the first story. The book and its mystique have long been a boon to the economy of Lee’s hometown of Monroeville, Ala., and now also to those stores that stocked the first copies of the new release. Fittingly, “Go Set a Watchman” went on sale when most watchmen are working – in the middle of the night.