Key PointsGreg Abel ended Berkshire's 14-quarter streak of net stock sales by purchasing approximately $19.8 billion more in equities than were sold in the second quarter.Form 13F filings allow investors to track which stocks Wall Street's savviest money managers have been buying and selling -- and Berkshire's will be filed after the closing bell today, Aug. 14.Although Abel was a big-time buyer of Alphabet stock in the second quarter, there are…