SAN FRANCISCO (Reuters) - Cindy Sheehan, the anti- Iraq war activist whose son was killed in the conflict there, put an end to speculation on Thursday that she would launch a long-shot bid to become a U.S. senator from California. Sheehan, speaking in front of San Francisco City Hall, said she would not run for the office. "If I thought that running for Senate would bring our young people home more quickly I would do it in a minute, but I am not convinced that that would do so," Sheehan said. A campaign would have pitted her against California's senior...