For at least the seventh time since November, a portable toilet was set ablaze near Russian Hill in San Francisco this morning, according to the fire department. The fire was reported at about 12:45 a.m. near the intersection of Union and Taylor streets and was nearly extinguished by the time firefighters arrived, according to a fire dispatcher. An arson team was out to investigate the scene, the dispatcher said. The fire department warned construction workers on Dec. 9 about an arsonist and asked them to keep the toilets locked and out in the open to prevent damage to surrounding objects....