By Herbert Lash NEW YORK (Reuters) – The dollar hit a four-year high as the yield difference between U.S. and German bonds widened the most in nearly 15 years on Thursday, while global equity markets fell sharply as the stronger dollar pointed to potential earnings losses. The strong dollar slammed oil and other commodity prices, spurred the safe-haven buying of gold and sparked a sell-off on Wall Street that tumbled the benchmark S&P 500 index 1.6 percent in the biggest single-day loss since July 31. …