ATHENS (Reuters) - Greek Socialists elected Finance Minister Evangelos Venizelos as their leader on Sunday, with a mandate to revive a party weakened by unpopular austerity policies ahead of parliamentary polls expected by early May. Venizelos, who has spearheaded the country's marathon debt talks, is set to resign from his post this week to focus on the general election, with all surveys showing the PASOK socialists badly trailing the conservative New Democracy party. ...