Fixing landscape spinner for iOS

[UIScreen mainScreen].bounds does not respect orientation.

Effect:
![bildschirmfoto 2014-03-25 um 20 04 22](https://f.cloud.github.com/assets/1731415/2516681/7b372b38-b450-11e3-9229-5105133c3ab9.png)

I took the solution from here: http://stackoverflow.com/a/12825439