Residents in two units of a Janesville apartment complex are displaced following a Friday morning fire.  The Janesville Fire Department says the sprinkler system at the River Flats Apartments activated and put out the flames by the time firefighters got to the scene.   The blaze at the building in the 200 block of North Jackson Street is limited to a closet. Two units suffered water damage, and firefighters help ventilate and remove water from the building.  Fire officials praise residents in the complex who helped evacuate the building and kept doors closed, limiting the spread of smoke.  The damage estimate is over 12-thousand dollars.  No injuries from the fire, and its origin is unclear..