HONG KONG — Global shares were mixed in holiday-thinned trading Monday, while oil prices fell after the OPEC+ group of oil producing nations said it plans to boost output. Markets were closed in Britain and much of Asia. The future for the S&P 500 slid 0.6% while that for the Dow Jones Industrial Average lost 0.5%. Germany’s DAX gained 0.4% to 23,181.61 and the CAC 40 in Paris slipped 0.4% to 7,737.21. U.S. benchmark crude oil fell as much as 4% early in the day. By late Monday in Asia it had shed $1.15 or 2% to $57.14 per barrel….