HANOI (Reuters) - A prominent critic of the Vietnamese government said he was taken by police from his home early on Tuesday so that he would be unable to meet U.S. President Barack Obama in Hanoi with other civil society figures. Nguyen Quang A said he was forced into a car by a group of police officers, driven out of the capital, and kept away for 5-1/2 hours.  During this time, Obama met six civil society leaders and later said several people had been prevented from meeting him. Obama said that despite great strides made by Vietnam, Washington had concerns about the limits it puts on political freedom. 