Michael Stravato for The New York Times In 1857, Mexican-American freight haulers were hanged on an oak tree at the courthouse in Goliad, Tex. GOLIAD, Tex., July 16 — In history books, the killing of more than 300 Texan rebels by Mexican troops here has long been known as the Goliad Massacre. But to many residents of Goliad, with its 18th-century Spanish fort and towering monument to the dead, that brutal episode in its history is still open to interpretation. At the heart of the dispute, largely between Anglos and Mexican-Americans, is the porous definition of who is a Texan...