* Treatment charges fall to two-year low - market * Charges near or below breakeven for some Asian smelters - analysts * Improving supply in 2013 will push charges higher - analysts By Silvia Antonioli and Felipe Iturrieta SANTIAGO, April 19 (Reuters) - Spot copper treatment and refining charges for copper have fallen to two-year lows that make it unprofitable for many Asian smelters to continue operating, miners and analysts said this week. Smelters' fortunes have taken a