Libya's long-neglected, isolated southern region has grown more lawless since the fall of Moammar Kadafi. Only ill-trained tribal militias hold Islamist extremists at bay.SABHA, Libya — Their fatigues don't match and their pickup has no windshield. Their antiaircraft gun, clogged with grit, is perched between a refugee camp and ripped market tents scattered over an ancient caravan route.