* Ramadi tribes turn on al Qaeda fighters
* Anbar violence is test of strength for Maliki
* Syria war feeding instability in Iraq
By Suadad al-Salhy
BAGHDAD, Jan 3 (Reuters) - Sunni Muslim tribesmen backed by Iraqi troops fought al Qaeda-linked militants for control of Iraq's western province of Anbar on Friday in a critical test of strength for the Shi'ite-led government of Prime ...