By Harry Robertson LONDON (Reuters) – A huge two-month rally in bond prices, powered by expectations that central banks will soon be cutting interest rates, has rescued fixed income markets from an almost unheard-of third straight year of declines. The U.S. 10-year Treasury yield, the benchmark for borrowing costs globally, has dropped 50 basis points (bps) in December after falling 53 bps in November. Its two-month fall is the biggest since 2008, when the Federal Reserve was slashing rates during the global financial crisis. ICE BofA’s global broad bond market index, which includes government…