For years she was tagged the "runaway nun," the rebellious ex-Catholic with outspoken opinions about religion--comparing, for example, Pope John Paul II to a Muslim fundamentalist.Now, with her 12th book, Islam, a Short History, Karen Armstrong has changed her image. She can still be sharp-tongued, inclined to draw conclusions that get a rise out of critics. But something closer to reconciliation, rather than anger, is propelling her. The title of her lecture is "Islam: A Short History."