_instances should return the list pre-sorted

Summary: You want the results sorted at least 90% of the time, so we should just do that and be done with it.

The complication, of course, is Computed Name. But that's an edge case -- not one Space in 20 is going to use it. And we can fairly easily and efficiently manage it otherwise, by pre-computing the inheritance tree (which we want anyway), and storing each node pre-sorted if that can be done efficiently. That would get us what we want most of the time, and speed up the system significantly. It seems like it's simply a win, so let's just do it.