By Elizabeth Dilts Marshall NEW YORK (Reuters) – World equities fell on Thursday to an 18-month-low, with markets dogged by fears high inflation would persist and force central banks to keep tightening monetary policy. In the United States, stocks ended a whipsaw session slightly lower, as investors juggled fears of nagging inflation with signs it could be peaking. The S&P 500 came within striking distance of confirming a bear market since swooning from its all-time high reached in January. In Europe, economic worries were exacerbated by a German warning that Russia was now using energy suppli…