FERGUSON, Mo., Nov 24 (Reuters) - A St. Louis-area grand jury was expected on Monday to resume deliberations over whether to bring charges against a white policeman who shot and killed a black teenager in a case that has triggered months of demonstrations and set the city on edge. With no one knowing how long that process might yet run, residents are anxious and shop fronts are boarded up in fear of unrest, while students in one school district began an extended early Thanksgiving break. The Aug.