For believers in the accuracy of opinion polls, the first inkling of Sinn Féin’s extraordinary electoral performance occurred during the final week of the campaign. For poll agnostics, the day of the count produced an outcome as politically jaw dropping as the day the Brexit referendum was carried or when President Trump was elected.  From now on, it is reasonable for Irish businesses to plan for the day that Sinn Féin holds the levers of tax power as the largest party in a coalition government or potentially in power on its own. So, what, according to their 110-page manifesto, are…