By Paul Taylor BRUSSELS (Reuters) - For the International Monetary Fund, five years of playing junior partner in European bailouts for Greece has been a "never again" experience, and the worst may be yet to come. The global lender has lent far more to Athens than to any other borrower, contributing nearly one-third of the total 240 billion euros, with the rest coming from euro zone governments and the bloc's rescue fund. Called in by EU paymaster Germany to try to keep the European institutions and the Greeks honest, the Washington-based IMF has never had control of the programme.