Flu Vaccine Failure Spotlights Faulty System By PAUL ELIAS     SAN FRANCISCO (AP) -- The crisis in the nation's flu vaccine supply has led to renewed calls to modernize a half-century-old manufacturing system that relies on millions of chicken eggs and a lot of educated guesswork.    Because it takes at least six months to produce the annual flu vaccine, no manufacturer can replace the 46 million shots Chiron Corp...