Add failing test demonstrating failure of complex union type.

We're doing some stuff with complex union types, and, unfortunately, it's failing validation when I don't think it should be.

I've added a failing test case demonstrating a case where it should pass validation but should not.  (Obviously, this PR should not be merged until somebody changes the implementation to make it pass).

I may get around to fixing this at some point but I don't have time right now, and I figure @hoxworth may be able to fix this much easier.