Quick fix apple retina


![after](https://f.cloud.github.com/assets/3518808/2365319/664307b6-a6bc-11e3-9226-7d3bd7c75ce7.png)
![before](https://f.cloud.github.com/assets/3518808/2365320/66453d92-a6bc-11e3-87b7-1f1420d2acc1.png)

artifacts remained on screen while moving the tool cursor. Solution: draw the cursor slightly smaller (see "before" and "after").