Rounding FUISwitch thumbEdgeSize calculation

Rounds down the thumbEdgeSize using floorf. Which without, you can see the rendering issue:

![screen shot 2013-05-17 at 21 50 31](https://f.cloud.github.com/assets/608543/520404/9889d7bc-bf37-11e2-812f-e4ced33a7dba.png)