In its 31st year, the Grant Park tradition takes on a New Orleans flavor. Aaron Neville and Dr. John headline on the final day, Sunday. Dr. John has been in the spotlight of late, recording a smokin' comeback album with Dan Auerbach of the Black Keys and dropping mystic food aphorisms on Top Chef. More Southern roots: The wonderful Carolina Chocolate Drops are penciled in for Friday. Bettye LaVette headlines Saturday, and the usual roster of local regulars fill in the gaps.