openlayers/ol3 — pull request #324 by twpayne (2013-03-08 13:43:12+00:00)
Title: Canvas renderer is not properly cleared

With the changes in #263, we are left with rendering artifacts like this:
![canvas-issue](https://f.cloud.github.com/assets/41094/235662/914cba44-87b7-11e2-907b-863b0f798d12.png)

(append `?renderer=canvas` to the full screen example and zoom in/out to reproduce)