I'd just like to point out what no one has said so far... Black people call each other that word all the time. "What's up my nigga?" "Yo nigga, come here!" Note: Black people only get upset when it comes from a non-black mouth. They can even tolerate it when it's being used by each other in the derogatory way, moreso than when it comes from a non-black mouth.
Granted, no one should really use it, but the word, due to its multi-use meaning, has lost a lot of its negative "powers". Only ignorant people get offended by the word being used in a book that was written before the Civil War, before it was deemed by society to be wrong to be used in a negative way anyway.
So, sorry to be rude and blunt, but get over the word, it'll probably still be around for a few more hundred years, if not longer. Don't clog up fiction site's with a whine about a book someone else wrote. Go on a blog and write your tangent there.