For a lot of New Orleans music fans, French Quarter Fest starts when Marc Stone kicks his band into high gear Friday morning at the Tropical Isle stage. The Gazebo has been his spot for nine years, a kind of unofficial start to the festival season, and this year he’s celebrating it with the strongest band he’s ever assembled and a deep book of originals highlighted by songs from his latest and best album, Poison & Medicine. It is certainly a magic moment after a lousy winter, with the war...