It's a coup for the Peabody Essex Museum. This summer, the Salem exhibit hall is the only place in the United States where you can see more than 100 works by the British master J.M.W. Turner. He's known for his landscapes, but the Peabody Essex is making waves with an unusual show looking at Turner's lifelong fascination with water. The show just opened last weekend, and WGBH News Arts Editor Jared Bowen has already seen it.