Handling of unknown names in QL is inconsistent

Summary: This the the straw that breaks the camel's back for the current behavior of, There is no Thing named "Foo" -- might be a typo?

The current behavior has always been controversial. What pushes it over the line is the fact that this error goes away if the name is formally defined as a Tag in some Property somewhere. Then, it suddenly behaves as such things do in a traditional Wiki. This inconsistency is so subtle and unobvious that it calls the whole thing into question.

So I think I'm just going to call this a misfeature and get rid of it. We'll see if that introduces any problems. I suspect that it will mean that, if you reference an unknown name and then have further Stages hanging off of it, you'll get more-cryptic errors, but let's address that a separate problem.