"void" enhancements

[jwatzman]

@elgenie tweaked the way we deal with void to be more in line with what you'd expect. We also reserved $_ to always be of type void. I think the spec goes on at some length about the issues with the former; we can remove most of that. Then we need to add the latter.

[RexJaeschke]

I've just made a pull request (Branch 008-Misc-nits-1) that cleans up the void-related stuff.