Fix C string lifting test.

I guess you can be clever, or ARC can be clever, but not both.

According to http://stackoverflow.com/questions/14186336/how-to-autorelease-a-non-returned-object-under-arc the autoreleasing `NSData` trick won't work in ARC. I guess it breaks on `Release` because the optimizer checks if you actually use the reference or not. There are some tricks posted on how to make it work anyway, by using a helper function, but I think this is clearer.