FORT STEWART, Ga. — A futuristic whirr from the skies cut through the quiet of an unusually cool Georgia afternoon. In stationary concentration, a soldier moved only his fingers as he steered a small device through plastic pipes arranged into a makeshift obstacle course built to qualify soldiers on a tool that has quickly changed the course of modern warfare: drones . Unmanned aircraft shape nearly every part of the battlefields today, from reconnaissance and artillery spotting to precision