BEIRUT, March 6 (Reuters) - About 100,000 people have fled to shelters in Lebanon and the number of displaced is expected to rapidly increase following "unprecedented" Israeli warnings ordering people out of large parts of the country, a senior U.N. official said on Friday.With war raging between Israel and Lebanon's Hezbollah, the Israeli military on Thursday ordered residents out of Beirut's southern suburbs, including areas controlled by the Iran-backed group, as well as parts of the eastern...