entvalidate.py, companion to checkrefs.py, is currently broken in several ways:
- It doesn't properly handle mixins / special templates
- On python 3.8+, XML elements are no longer sorted and this fails validation against entity.rng
- mixins are not properly applied because the | split is incorrect (3 max items instead of 2)
- merge="" is not supported
- Parents aren't always passed when they should be.
This fixes all these issues.