By Martin Dokoupil DUBAI, Sept 24 (Reuters) - Saudi Arabia's eco**mic growth eased to an annual 3.8 percent in the second quarter of 2014, the lowest rate in a year, because of a slowdown in the oil sector, official data showed on Wednesday. But the first-quarter growth rate for inflation-adjusted gross domestic product was revised up to 5.1 percent - the fastest pace since the third quarter of 2012 - from an initial reading of 4.7 percent. On a quarter-on-quarter basis, GDP dropped 3.1 percent in the second quarter, the biggest fall since the quarterly data ****** began in 2010, after a 4. ...