SALAMANCA — A long-missing peace pipe tomahawk President George Washington gave to a Seneca leader in the late 18th century has been returned to the tribe in western New York.Washington gave the combination tobacco-smoking pipe and weapon to Cornplanter as the United States negotiated a peace treaty with the Six Nations of the Iroquois Confederacy.The artifact eventually wound up at the State Museum in Albany, where it remained until being stolen in the late 1940s.