Digest broken table and tr attributes

This avoids foster-parenting diffs like this:
https://fr.wikipedia.org/w/index.php?title=Aquila_Italiana&diff=101605787&oldid=90404051

We should separately check why selser did not handle the foster-parented
content correctly.

Change-Id: Ia5a5bb6b4063438f65fed26e1acb8b844c147a01