change optimisation level as recommended for Data.Vector
change optimisation level as recommended for Data.Vector

Ignore-this: b7458255b3b500fd0c8cc9b4644e8039

darcs-hash:20100224062743-9241b-014b040cce52610f01513a66b9f870a6626c3fa4.gz

tmcdonell/hfx,tmcdonell/hfx,tmcdonell/hfx