Using a ProxyArray to get ListBox items handled correctly

Meant to not make a new branch, but I accidentally screwed up the old one when trying to revert it and decided to delete it. (See #992).

Anyways, to repeat: this intends to address #820.

This time my approach is an ArrayProxy that inherits from BasicObject and delegates everything to Array. 

Please let me know if this approach is good, needs tweaking, or needs a totally new direction (for example, how about `class ProxyArray < Array`?).

I have some questions / comments. I'll put those in-line before :poultry_leg: :sweet_potato: :fork_and_knife:  time!


Using `to_a` as the method for returning the inner array seems totally conventional use of Ruby semantics--anything "arrayable" generally turns itself into an array via `to_a`, and this seems no different.

I also don't see it as a problem that for testing or other spots we might need to do that conversion.

Would like to understand a little more what the test initialization failures were, though.