Addresses potential issues in the APC & APCu cache drivers when different APCu versions are in use (and depending on PHP configuration this can affect the APC driver even though all fixes are related to the APCu extension).
Testing Instructions
I only hit this by fixing various unit test issues that caused many adapters to not be tested, I don't have user level instructions for this. I can tell you though that if you apply only the patch for the unit test file and run the cache tests if you have the right APCu version installed you can trigger the "undefined index" errors that this fixes.