Stocks turned mixed around halftime Wednesday, erasing some losses after House Speaker John Boehner said he was optimistic that Washington could make a deal to avoid the fiscal cliff. The Dow Jones industrial average rose 0.1%, while the S&P 500 dipped 0.1%. The Nasdaq slipped 0.1%, after being down nearly 1.1%. Volume was tracking up slightly from Tuesday's levels on both main exchanges. On the downside, DaVita HealthCare Partners (DVA) fell 2%