Clear our canvas bitmap before scaling.
Clear our canvas bitmap before scaling.

This avoids leaving garbage pixels in place on non-Retina displays (and in
simulator).

rachelharvey/playn,ruslansennov/playn2,longtaoge/playn,thecocce/playn-1,thecocce/playn-1,ruslansennov/playn2,playn/playn,playn/playn,rachelharvey/playn,longtaoge/playn,playn/playn,tinkerstudent/playn,tinkerstudent/playn