The Whitney Museum of American Art has been having trouble keeping up with the demand to see “Jeff Koons: A Retrospective,” an exhibition that fills most of the museum’s space and was described by Roberta Smith in The New York Times as “the most cogent account of Mr. Koons’s career in over two decades.” And it may be that museumgoers want a last chance to walk through the Whitney as it is currently constituted, before the museum leaves its Marcel Breuer building for its new home, designed by Renzo Piano, in the meatpacking district.