Bgerstle/desc fix

For example, if an `OCClassMockObject` is inside an `NSDictionary` and some part of the test code calls `-[NSDictionary description]` (for example, when logging the contents of the dictionary to the console), then these isNS*__ methods are called on its contents.  This appears to only be an issue on iOS 6, which is why `UIDevice` is used to detect `systemVersion` at testing time.

It's reasonable to expect this to be tolerated since it shouldn't have any effect on test results, and is simply an annoyance to the tester to write extra for stubs for things that aren't relevant to the test.