By Tetsushi Kajimoto and Izumi Nakagawa TOKYO (Reuters) - The Japanese government upgraded its assessment of the economy on Monday, as emerging signs of an upturn in exports and factory output added to growing evidence that Prime Minister Shinzo Abe's aggressive polices are beginning to reignite growth. The world's third-biggest economy is gradually recovering, according to the government's monthly report released by the Cabinet Office. The upgrade was the first in two months, and an improvement from April when it said the economy was showing signs of recovery but still had some weak spots. ...