With the stock market in turmoil, it’s a good time to check in on what Warren Buffett is doing with his portfolio. Buffett’s Berkshire Hathaway Inc. (NYSE:BRK.A, BRK.B) has struggled in the first half of the year. Money Morning’s Jason Simpkins says $3.5 billion of Berkshire’s recent $4-billion shopping spree is still unaccounted for…