By Lefteris Papadimas and Deepa Babington ATHENS (Reuters) - Former Greek Prime Minister George Papandreou says his newly-formed party is open to an alliance with election frontrunner Syriza as long as it agrees to hold a referendum on reform policies after Sunday's election. With a firmly pro-euro and pro-reforms platform, Papandreou could be a moderating influence on Syriza, whose radical ...