(Reuters) - Egyptian police battled thousands of protesters outside President Mohamed Mursi's palace in Cairo on Tuesday, prompting the Islamist leader to leave the building, two presidential sources said. Police fired teargas at demonstrators angered by Mursi's drive to hold a referendum on a new constitution on December 15. Some broke through police lines around his palace and protested next to the perimeter wall. Several thousand people had gathered nearby in what they dubbed "last warning" protests against Mursi, who infuriated opponents with a November 22 decree that expanded his powers. "The people want the downfall of the regime," the...