GLOBAL MARKETS-Stocks gain; doubts arise on end to Fed purchases

* Benchmark stock indexes rise; renewed doubts on stimulus cuts * Treasuries prices rise on disappointing U.S. home sales * U.S. dollar index gives up gains NEW YORK, Aug 23 (Reuters) - Benchmark stock indexes around the world edged higher on Friday, while the dollar fell after a U.S. government report on new single-family home sales raised doubts about the timing and extent of cuts to the Federal Reserve's stimulus program. New home sales dropped 13.4 percent in July to an annu