PHILADELPHIA (Reuters) - The Federal Bureau of Investigation unveiled a new unit on Wednesday to tackle the multi-billion dollar market in stolen art and announced the FBI's first recovery of artifacts looted from Iraq after the U.S. invasion. The objects, eight Mesopotamian stone seals about 5,000 years old, were purchased in Iraq by a U.S. marine as a souvenir of his tour of duty. He handed them to the FBI in Philadelphia after an archeologist confirmed their authenticity and said they had been stolen from one of Iraq's many archeological sites. The soldier paid a trinket salesman about $300 for...