By Amanda Ferguson BELFAST (Reuters) -Sinn Fein, the former political wing of the Irish Republican Army (IRA), hailed its first victory in a Northern Ireland Assembly election as a “defining moment” for the British-controlled region and called for a debate on a united Ireland. Sinn Fein was ahead of the pro-British Democratic Unionist Party (DUP) by 27 to 24 seats with two left to declare, making it the first Irish nationalist party to become the largest in the devolved assembly. “Today represents a very significant moment of change. It’s a defining moment in our politics and for our people,” …