WASHINGTON (Reuters) – President George W. Bush, who will host a global summit on the financial crisis next month, said on Saturday that agreeing on common principles to reform regulators would be essential to preventing another disaster. His comments came one day after a worldwide sell-off in stock markets amid growing fears of a global recession. Friday's session was the lowest closing level for all three major U.S. stock indexes since the spring of 2003. "In recent weeks, concerns about the availability of credit, the safety of financial assets, and the volatility of the stock market have made many families...