Venezuelans Vote to Keep Chavez in Office CARACAS, Venezuela - Venezuelans overwhelmingly voted to keep President Hugo Chavez in office, dealing a crushing defeat to a splintered opposition and allowing the leftist leader to convert one of the biggest challenges of his presidency into an even broader mandate to carry on his "revolution for the poor."   Stunned opposition leaders, who have fought for years to oust Chavez, claimed fraud after results announced Monday by election officials showed nearly 60 percent of voters had said "no" to the question of whether he should leave office immediately.    But former President Jimmy Carter and the Organization of American States endorsed the results of Sunday's vote, which saw one of the biggest turnouts in Venezuela's history, and urged everybody to accept the outcome...