Boston authorities are probing three separate Dorchester shootings yesterday that left one person with life-threatening injuries, and two women and a teen wounded.The spate of gunplay began early yesterday morning on Westville Street in Dorchester in what police said may have been fallout from a neighborhood cook-out.The injuries to the victims — a woman in her 30s and another in her 50s, and a male in his late teens — were not life-threatening, said officer Neva Coakley, a spokeswoman for the Boston Police Department.