WASHINGTON, Nov 6 (Reuters) - President Barack Obama said on Friday the jump in the unemployment rate to 10.2 percent in October was a "sobering" figure that underscored the economic challenges ahead. Obama, speaking after the U.S. jobless rate unexpectedly rose to a 26 1/2-year high, also said he had signed a bill that extended jobless benefits and homebuyer tax credits. "I just signed into law a bill that will help grow our economy, save and create new jobs and provide relief to struggling families and businesses," Obama said in a statement delivered in the White House Rose Garden. "The...