TAIPEI, June 11 (Reuters) - Bailed-out U.S. insurer American International Group and the buyers of its Taiwan Nan Shan insurance unit have modified the terms of a stalled $2.2 billion deal to speed up its passage by Taiwanese regulators. AIG said on Friday $325 million of the purchase price would now be placed in escrow for four years on completion of the deal as an additional measure of support ...