ATHENS (Reuters) - Former Greek Prime Minister Alexis Tsipras' Syriza party would get 29 percent of the vote in a Sept. 20 snap election, versus 27.8 percent for the conservative New Democracy party, an opinion poll by Metron Analysis showed on Friday. Popular Unity, a party formed last week by disaffected Syriza rebels who oppose the country's latest 86 billion euro bailout, would be backed by 4.1 percent of those polled. Far-right Golden Dawn ranked third, at 8.3 percent, followed by centrist Potami which would get 6.7 percent. ...