(28 Aug 1997) Eng/Serbo-Croat/Nat NATO-led troops dispatched to prevent violence between rival Serb factions fired tear gas and warning shots on Thursday to fend off a crowd hurling stones and firebombs. At least one U-S soldier and several civilians were wounded in one of the most serious confrontations between foreign troops and civilians since the 1995 Dayton peace accord. S-FOR troops are in Bosnia to keep the peace. Here in Brcko they've become the target of attack. The NATO-led troops