Most of what needs to be said about the NewSouth edition of Mark Twain's The Adventures of Huckleberry Finn is being well said elsewhere. Maybe some 2¢ to be added.
1. This kind of thing is not new at all. And the fact that a lot of older attempts to neuter literary works have been forgotten may be a good sign.
2. It must be said: "nigger" is absolutely vital to the story of Huck, Jim, and Tom. There are things you don't do to a man, not if you call him "man". You have to call him something else. Substituting "slave" doesn't cut it. It doesn't tell you why just about everyone in this fictional world is content to have blacks enslaved.
3. Schoolchildren who read the expurgated version will be confused to see slave owners and other questionable Old South people avoiding the slur. Especially if they know/find out that the scummier edges of the blogosphere routinely use it to describe the President of the United States. (No need for links. You know how to use Google.)