-- Fears that gang violence is on the rise in Boston's southern neighborhoods seemed justified as police revealed that Monday's shooting of a five-month-old baby in Mattapan may have been part of a cycle of retaliatory killings between rival Jamaica Plain gangs. Police believe that the shooting, which left Alianna Peguero in the hospital, may have been a retaliation for the April killing of Luis Troncoso on a basketball court in JP. The Troncoso killing,......