Allows requesting of 'When in Use' when compiling with the iOS 7 SDK but run on iOS 8.

You may find this change useful, especially during the transition from iOS 7 -> 8.

If your app isn't compiled with the 8.0 SDK, but runs on iOS 8, it will default to requesting for "always authorization." That is expected behavior, but kind of sucks for the developer if you just wanted to request for "when in use".

This change makes it so if the `locationManager` has the new APIs, it will use them, but if not, it will continue to behave as a regular pre-iOS 8 app would.

Considering all this, it may be a good idea to also remove that `NSAssert` if neither key is found in the Info.plist file. Since it is possible an iOS 7 app was built without these keys, and it would just start crashing on iOS 8 without much warning. I'll let y'all make the call on that one, though. Just let me know if you'd like it removed.