By Philip Pullella VATICAN CITY (Reuters) -Pope Francis has decided to return to Greece three 2,500-year-old pieces of the Parthenon that have been in the papal collections of the Vatican Museums for more than a century. The Vatican said in a brief statement on Friday that the pope was giving them to Ieronymos II, the head of the Greek Orthodox Church, as a gesture of ecumenical dialogue with the Roman Catholic Church. The Parthenon, which is on the Acropolis in Athens, was completed in the fifth century BC as a temple to the goddess Athena, and its decorative friezes contain some of the great…