A nearly three-year effort to put a strong anti-human-trafficking law before voters succeeded this week, organizers said, when they counted 873,000 signatures on their petition to put the proposed Californians Against Sexual Exploitation Act on the November state ballot. The citizen-led campaign to strengthen criminal penalties against people who traffic teenagers, children and immigrant laborers on the streets of California cities, and over the Internet, has been working on the issue since 2009, when some Fremont residents started a grassroots organizing effort.