WASHINGTON – Former Sen. John Sununu, a member of the government watchdog panel that oversees the financial sector rescue fund, is joining the board of managers of a firm affiliated with a bank that has received $3 billion from the fund. Sununu last week was named to the board of ConvergEx Holdings LLC, the holding company for BNY ConvergEx Group. The Bank of New York Mellon Corp. holds a 33.8 percent stake in BNY Convergex, but it has no control over the company or its board. The bank was one of nine institutions selected by the Treasury Department last fall...