By Cheney Orr ATLANTA (Reuters) – A protest in Atlanta briefly turned violent on Saturday as demonstrators set a police car on fire and smashed windows of buildings. Marchers had gathered to protest the killing of an activist by law enforcement on Wednesday during a raid to clear the construction site of a public safety training facility that activists have derided with the nickname “Cop City”. The demonstration started peacefully, then abruptly escalated with some protesters throwing fireworks and rocks and smashing buildings’ windows with hammers, according to a Reuters witness. As police mo…