Updates to multi-level inheritance support.

* Down-cast to final level even if we can't select the related data (in < 1.6).
* Change tests to use the grand child even in < 1.6.
* Fix bug where child classes are accepted if grand-child doesn't match even if
    there are more grand-child classes to check.
* Add test for this bug.
* Fix test to not pull in children while pulling in grand-children.
Add related inheritance subclasser.