By Edward McAllister NEW YORK (Reuters) – Google Incs Street View cars have captured the worlds roads, highways and back alleys for years. Now they are being used for something entirely different: detecting the thousands of natural gas leaks blighting major U.S. cities. Google cars fit with air monitors have taken millions of readings along the streets of Boston, New York and Indianapolis over the past two years as part of a program run by the non-profit Environmental Defense Fund to help reduce methane emissions. In central Boston, leaks were discovered every few blocks.