SAN FRANCISCO (Reuters) - In a career marked by second acts, Al Gore, the former vice president of the United States and co-winner of the Nobel Peace Prize, is becoming a partner at Silicon Valley's most storied venture capital firm. Kleiner Perkins Caufield & Byers said on Monday that Gore, a campaigner for action to slow global climate change, will join the Menlo Park, California-based venture capital firm as a partner focused on alternative energy investments. The venture firm, which since 1972 has backed seminal computer start-ups ranging from Sun Microsystems to Compaq Computer to Amazon.com to Google Inc, has...