After a 14-minute battle involving five bidders — four on the phone and one in the room — a new auction high was set for the French Impressionist Claude Monet on Wednesday evening when the artist’s radiant 1891 canvas “Meule,” or “Grainstack,” fetched $81.4 million with fees at Christie’s in Manhattan. “The Impressionist market is alive and well,” said Brooke Lampley, head of the Impressionist and Modern Art department at the auction house.