example of /#797

example which makes polygon artifacts @aesnyder

mashed back and forth clear and add button or zoom in at out

darker double poly layers
![screen shot 2014-12-05 at 5 13 54 pm](https://cloud.githubusercontent.com/assets/583593/5323836/316d791a-7ca2-11e4-9ba3-1d8cf21077a8.png)

post clear

![screen shot 2014-12-05 at 5 14 10 pm](https://cloud.githubusercontent.com/assets/583593/5323841/35cf2058-7ca2-11e4-8573-db58c790af21.png)