As New York City’s museums gear up for major exhibitions dedicated to major talents — most notably, “Manet/Degas” at the Metropolitan Museum of Art, as well as “Barkley L. Hendricks: Portraits at the Frick,” MoMA’s “Picasso at Fontainebleau,” and “Max Beckmann: The Formative Years, 1915-1925” at the Neue Galerie — not a few commercial galleries are dedicating their fall schedules to veteran artists whose work is testament to dedication sustained over the long haul. Living artists, in other words, have got it going on.