By Francesco Canepa FRANKFURT (Reuters) – The world’s top central bankers are beginning to fear that an already weak global economy will stall if they keep pressing on the brakes, unnerved by plunging commodity prices, turmoil in emerging markets and potential flashpoints at home. Central bankers in the euro zone, United States, Canada and Australia have all been hinting that the bigger part of their series of aggressive rate hikes may be behind them even though inflation remains high. This has fuelled market speculation that central banks may be heading for a “pivot”, market parlance for a ch…