* Gains led by futures -analyst * Banks and carmakers jump, yen hits 94 to the dollar * DeNa loses out as poor overseas performance highlighted By Tomo Uetake TOKYO, Feb 18 (Reuters) - Japan's Nikkei share average jumped 2.3 percent by the midday break on Monday, led by exporters and banks after the yen softened following the G20's decision not to single out Japan for adopting policies that weakened its currency. The Nikkei added 251.61 points to 11,425.44, with financials a