A long-standing conflict in the multi-ethnic flashpoint town of Tuz Khurmatu exploded into sustained violence late Saturday night and Sunday, as several forces nominally allied against the so-called Islamic State (IS) group turned their guns on one another.Reinforcements were called in, despite an attempt at a cease-fire, risking the most severe escalation of sectarian fighting in Iraq’s disputed territories since November, when the same groups securing the same town became temporary enemies…