Buffett continues his buying spree in Occidental Petroleum.Taking a look at what the smart money is doing on Wall Street can prove to be a useful exercise for investors. Following the end of each quarter, institutional investors such as hedge funds and wealth management firms are required by the Securities and Exchange Commission (SEC) to file a form called a 13F.  It documents all the buying and selling activity from large, sophisticated investors, and provides a glimpse into where meaningful flows of capi ...