Move away from obj->isa, and wrap the workAroundMacOSXABIBreakingBug...

...check with a diagnostic ignore (bitmasking tagged pointers is deprecated).  

There's likely more work to do around the ABIBreakingBug check; primarily wanted to get this up and running on iOS/Xcode5.0.1.  Tested on iOS7.


this wont work on 64bit iOS devices.