BEIJING (AFX-ASIA) – Warren Buffett’s holding company Berkshire Hathaway Inc paid about HK$1.42 billion to double its stake in PetroChina Co Ltd (HK 0857; NYSE PTR) to over 13% of the state-owned oil producer’s Hong Kong-traded stock. (US$1=HK$7.78). The purchases last month in the listed unit of China’s biggest oil producer are likely a reflection…