By Amanda Ferguson BELFAST (Reuters) -Sinn Fein, the former political wing of the IRA, looked set to claim top spot in elections in British-controlled Northern Ireland for the first time on Friday, a historic shift that could bring the once-remote prospect of a united Ireland closer. Sinn Fein secured 29% of the first-preference vote compared with 21.3% by the pro-British Democratic Unionist Party (DUP), indicating it was likely to become the first Irish nationalist party to win the most seats in an election to the regional assembly since the state’s creation in 1921. “Sinn Fein on course to h…