Copy prototype bug with enumerable properties

Per [this thread](https://github.com/angular/angular.js/commit/b59b04f98a0b59eead53f6a53391ce1bbcbe9b57#commitcomment-6844633)

Creating a placeholder for a possible fix which includes associated tests.
@gentooboontoo - no, we only want to consider enumerable properties. I think we're close to a solution with [this](https://github.com/angular/angular.js/pull/8032#issuecomment-47670910)