UPDATE 1-Iraq's Sadr calls on rival to join him in ousting PM

Populist Iraqi Shi'ite cleric Moqtada al-Sadr has invited his biggest political rival to work with him on ousting the country's prime minister as thousands of anti-government protesters took to the streets for a fifth day.In a statement on Tuesday Sadr, who leads parliament's largest bloc, asked Hadi al-Amiri, leader of the second-largest, to help him introduce a vote of no confidence in Prime Minister Adel Abdul Mahdi."To answer brother Abdul Mahdi, I thought asking you to call an early electio