By Emily Le Coz JACKSON, Miss. (Reuters) - Tornadoes unleashed by thunderstorms along the U.S. Gulf Coast ripped through southeastern Mississippi on Tuesday, killing four people, injuring many and causing extensive damage, authorities said. One of the heaviest-hit areas was a commercial district along a U.S. Highway 98 bypass in the town of Columbia in Marion County, about 30 miles (48 km) west of Hattiesburg, state emergency management spokesman Greg Flynn told Reuters. ...