In a quarter highlighted by the often-promised, finally delivered start of interest rate hikes by the Federal Reserve, the average stock mutual fund ended it higher despite a rough December. U.S. diversified stock mutual funds leapt 6.18% in October. Losing steam, they inched up just 0.78% in November. And then they plunged 2.80% last month, according to preliminary Lipper Inc. data. That left U.S.