June begins, the art world convenes briefly in Basel and then prepares to break for summer. But wait. An art dealer’s job is never done, especially in this superheated art market. Off they go to London, to spend the summer solstice at Sotheby’s and Christie’s June auctions of Impressionist, modern and contemporary art, whose totals these days are within hailing distance of the big May sales in New York. It’s a great time to be an art dealer.