LONDON (Reuters) - The U.S. Federal Reserve's efforts to shield the economy from the effects of the coronavirus have -- for now - slowed a scramble for dollars that threatened to clog funding markets.The dollar had gained almost 9% in 11 days in the rush for cash, but it fell on Tuesday, at one point to its weakest since March 19 . Measures of demand for dollars signalled that many businesses and banks felt they had enough for now.The Fed announced on Monday it would buy bonds in unlimited..