This also will add mouseovers with the original text.

We already ignore the immediate children of script, form,
etc. elements, as well as spans that we've inserted ourselves.  This
change makes us skip the entire subtree of such an element.

One important effect is that if another extension changes one of our
spans using a similar algorithm to ours (inserting a new subtree) we
previously could end up reprocessing that node in a future
document_end event.  Now, we prevent that.

Use small-caps font-variant to fit in better with text on page