Avoid stack overflow when comparing objects with cycles (like DOM Elements)

[jpbochi]

[jpbochi]

@markstos yes, here's the pull request. You could try to get it merged. Or you could just use my version. :laughing:

But to be honest, this code* is far too messy. It cries for some unit tests. I wouldn't use it for production purposes.

• both the original and my changes.