Adding some tweaks required for the unit tests to complete on MacOS X 10.8.  They would run on the iOS7 simulators but not OSX directly; some tests would end up in infinite recursion.  Using [NSObject class] directly avoids the chance we are using a class which has had all its methods covered up when obtaining the objc_msgForward function, which seemed to be an issue.  Added isBlock to the white list as well, since that would also recurse infinitely otherwise.  With these changes, all the tests pass cleanly when running on 10.8, which none of the OCMock3 versions had for me.
Merge pull request #116 from carllindberg/RunOnMountainLion

Tweaks to allow running on MacOS X 10.8