Improve search for changed part

Find changed but childless element, e.g. div → p, header → h1, ul → li,
dl → dt;
otherwise, keep scroll in place;
still in some cases it wouldn’t work, e.g. ul → li → ul → li — first li
has child, but also its own content, so if first li was changed (add
some text), then MV won’t know about this, because the actual content
does include child’s content as well.
It would be so much simpler if they wrapped every text block
in <p></p> :unamused: