The Oracle of Omaha has been a big-time seller of stocks for 10 consecutive quarters -- but there's one sale he may regret.There's arguably no announcement that's packed with more information and clues about the stock market and the companies powering it higher or lower than quarterly Form 13F filings with the Securities and Exchange Commission (SEC).13Fs are filed no later than 45 calendar days following the end to a quarter by institutional investors with at least $100 million in assets under management. ...