Warren Buffett, true to form, was busy buying stocks as the market retreated. He says that Berkshire Hathaway (BRKB) has dived deeper into IT giant IBM (IBM) this quarter. The investment comes after Berkshire recently ploughed $4.5 billion into oil refining company Phillips 66 (PSX) and agreed to buy aerospace and industrial supplier Precision Castparts (PCP) for $32 billion. Berkshire…