title: iPhone : changing background image when rotating device using size classes
body: <p>I placed a background image that needs to fill the iPhone screen. It is fine in portait view but when I rotate the device the top is cropped which I don't want.
  The best seems to be an image for the portrait view and one for the landscape view.
  I tried to use the size classes, assigning 1 image for compact W and any H and 1 for any W and compact H. I can't make it work.
  I am using Xcode 6.3 and swift 1.2.
  I made another app using the instructions in the book iOS 8 essentials (Neil Smyth) chapter 24 but it does not work. I downloaded the file "universal_images", thinking I was doing something wrong but it does not work neither.</p>