SAN JOSE, Costa Rica (Reuters) – A protege of outgoing President Oscar Arias could be elected Costa Rica's first woman head of state on Sunday, though a conservative rival has upped his challenge ahead of the election. Opinion polls show ruling party centrist Laura Chinchilla, who has promised to expand Costa Rica's free trade pacts beyond the Western Hemisphere, within striking distance of the 40 percent of the vote needed to avoid a second round run-off. A late surge by libertarian Otto Guevara, who wants to replace the local currency with the U.S. dollar and crack down on rising crime,...