Yeah, I thought this was absolutely ridiculous the moment I heard it in the news a couple of days ago. It was what Mark Twain wrote. Get over it. Not only does 'slave' not have the same effect, but come on, now -- it's almost patronizing. We're all old enough to know naughty words; we're big boys and girls now. If anybody's offended, then put the book down and go read Pride & Prejudice. Sorry you can't accept basic history.
Because that's exactly what it is. Yes, it's an offensive word now, but we have to accept the fact that once upon a time, it was in very regular usage in everyday language. Erasing all instances of it in Huck Finn seems like erasing history. (Templars. Whaddya gonna do.)
However, I'd be supportive of an edited text of this kind for primary school kids if they were studying Huck Finn (I know of no school, but there'll be one somewhere), because a ten year-old kid might not fully grasp the concept or seriousness of the word, but definitely not for basic editions you can go out and buy. Twain would be laughing at all this.