NEW YORK (REUTERS).- The spotlight at this week’s post-war and contemporary art auctions at Christie’s and Sotheby’s is trained on star offerings such as Jasper Johns’ “Flag” and Andy Warhol’s “Self Portrait.” But the most unusual work could be Yves Klein’s monumental “ANT 93, Le Buffle (The Buffalo),” which is hitting the block for the first in its 50-year life on Tuesday. The rare work from the French artist’s signature “Anthropometrie” series is big, bright blue, and highly conceptual. Long before Jeff Koons floated basketballs in distilled water and Damien Hirst sliced up a cow and suspended it in formaldehyde, Klein donned a tuxedo and presided over a scene featuring an orchestra’s one-chord musical performance as a bevy of naked beauties strode before a Parisian gathering, smeared blue paint on themselves and proceeded to writhe on a large