Add more complete support for landscape orientation on IOS.  Also,
assume portrait mode if UIDeviceOrientationUnknown is returned from
the following call...

[[UIDevice currentDevice] orientation]

Testing:
  - IOS 7.1 on iPhone 5
  - IOS 7.1 on iPad 3
Merge pull request #25 from jmelvin/master

Add more complete support for landscape orientation on IOS.