By Marc Jones LONDON (Reuters) - Shares and bonds rallied globally on Thursday and the dollar tumbled, after the head of the Federal Reserve signaled the U.S. central bank may not be as close to winding down its stimulus program as markets had started to believe. This came despite minutes showing half of Fed policymakers think the program should stop by the end of this year. As investors cheered the prospect of ongoing support, risk assets performed strongly. European bonds from Germany to Greece tracked gains in U.S. ...