Handle new iOS 8 orientation enum value

I don't know what "<a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIApplication_Class/index.html#//apple_ref/c/econst/UIInterfaceOrientationUnknown">unknown</a>" orientation is, but there's a build warning now!

<img src="http://cl.ly/image/3h1C3D3U3n1y/Screen%20Shot%202014-09-22%20at%2016.35.16.png">