Sept 3 (Reuters) - The U.S.-trained Afghan pilots and others held at a camp in Uzbekistan already feared being sent back to Taliban-ruled Afghanistan. So it was little comfort when an Uzbek guard unsympathetically quipped the other day: "You can't stay here forever." The offhand warning added to an already grinding sense of unease at the camp just across Afghanistan's northern border, recounted one of the Afghan pilots who fled there with aircraft when ground forces fell to the Taliban in August as the United states and its allies withdrew their forces. What follows is the first, detailed inside account...