BJ's Wholesale is quietly outperforming the S&P 500.When it comes to warehouse retailers in the U.S., much of the investor focus out there centers on Costco Wholesale (COST -0.16%) or Walmart's (WMT 0.45%) Sam's Club. With locations in almost every state in the U.S., have a much more noticeable public presence.Because of that focus, investors may have missed the fact that there is a third player in the warehouse retailing market. They also have missed the stock price growth in BJ's Wholesale (BJ -3.97%).Alt ...