FERGUSON, Mo. — Unrest returned to the streets of this St. Louis suburb early Saturday as hundreds of demonstrators, angered by the shooting death of an unarmed African-American teenager by a police officer, engaged in a standoff with the police that was punctuated by threats and a new round of denunciations of law enforcement practices. The confrontation, the first serious one since the Missouri State Highway Patrol on Thursday assumed responsibility for security operations here, ended at about 4 a.m. when the authorities, prompted by the gradual dispersal of demonstrators, pulled back to their nearby command post. The Associated Press...