LONDON (Reuters) - Sterling faltered on Thursday and Europe's main stock markets went in and out of the red as hopes for a smooth Brexit ran into familiar Irish border snags.Asia earlier saw a five-day stocks rally grind to a halt as Wednesday's disappointing U.S. retail sales data on spread gloom, including to the dollar, though even there traders were watching Brexit.Ongoing Brexit talks passed various deadlines, but the main development was Northern Ireland's Democratic Unionist Party saying..