Test262: Potential __proto__ state leakage

[BobVarioa]

I'm not sure if this breaks anything right now, but in #138 I ran into the issue of var __proto__ = ... which assigned to the environment's object's __proto__ instead of being a normal key in an object. This probably affects more things as well.
This likely could also affect funcIndex, locals and globals. Perhaps, other things as well. This should be a relatively simple fix, just switching them to maps