ALTAR VALLEY, Ariz (Reuters) - U.S. Border Patrol agent Galen Huffman leans over the saddle to look at faint tracks in a cattle trail leading up from the Mexico border. He follows the tracks at a brisk trot through thick brush, up and down into rocky washes, then pauses as his horse twitches its ears and turns around nervously. "I have bodies," he says, as the first of a group of 11 illegal immigrants ... peel themselves up from the desert floor several miles from the nearest road. Horses have been part of the Border Patrol since the agency was...