Although share repurchases have slowed this year, exchange traded funds focusing on buybacks, including the PowerShares Buyback Achievers Portfolio (NYSEArca: PKW) and the SPDR S&P 500 Buyback ETF (NYSEArca: SPYB), have been solid performers. For example, PKW, the largest buyback ETF, is higher by 10.4% year-to-date. The extended low-rate environment in the wake of the…