Tesla will release earnings after the market closes Wednesday. While investors will be watching production numbers and cash burn, CEO Elon Musk is watching short-sellers. In his crosshairs is hedge fund manager David Einhorn, who said his wrong bet that Tesla stock would fall was a big reason for his fund's poor performance in the second quarter. Musk took a jab at Einhorn on Twitter Wednesday, offering to buy him a box of "short shorts."