New tests doc-before-include.json and doc-before-pragma.json show we
fail to reject a misplaced expression comment.

New test doc-no-symbol.json shows a bad error message.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <1489582656-31133-31-git-send-email-armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>