John Boatright might be the most versatile soldier who has enlisted in the current battle between Atlanta-based Delta Air Lines and Hartsfield-Jackson International Airport. Inthe past six years, Boatright has retired from Delta, presided over major parts of the city-run airport's multibillion-dollar expansion, and now has suddenly become the bare-knuckled heavy for — of all folks — Delta, which is trying to pare that massive construction initiative as it negotiates a new lease with the airport.