LONDON (Reuters) - A possible Nigerian link to attackers suspected of hacking a soldier to death in London while shouting Islamic slogans is being probed, two sources with knowledge of the investigation told Reuters on condition of anonymity. Two suspects have been taken into custody after the attack, which the British government said appeared to be an act of terrorism. Police have not identified the suspects. The sources, speaking independently, said a Nigerian link was being investigated but gave no further details about the nature of the link. Police spokesmen declined to comment. ...