RENO, Nev. — The U.S. Forest Service has built a new corral for wild horses in Northern California, which could allow it to bypass federal restrictions and sell the animals for slaughter. The agency acknowledged in court filings in a potentially precedent-setting legal battle that it built the pen for mustangs gathered in the fall on national forest land along the California-Nevada border because of restrictions on such sales at other federal holding facilities. The agency denies claims by horse advocates it has made up its mind to sell the more than 250 horses for slaughter.