A shootout between rival gangs in Mexico City left six people dead and four wounded, and police in the north-central state of Guanajuato found two heads and bags of severed body parts scattered on roadsides in two cities there. The violent and fast-growing Jalisco cartel has been expanding into both Mexico City and Guanajuato, though it was unclear immediately who was responsible for the killings. Guanajuato state prosecutors said the gory discov…