Deadly fighting broke out Thursday in the flashpoint town of Tuz Khurmatu between Kurdish security forces and al-Hashid al-Shabi militiamen, threatening to shatter a fragile alliance among fractious groups nominally united against the Islamic State (IS) organization.In sustained battles, both sides have used small arms, and Hashid militiamen say they used rocket propelled grenades (RPGs) to attack Kurdish security forces guarding a hospital. Multiple people have been killed on all sides – Ku…