(Bug 4868) Display the name even for external site tags

We strip_html in some places where we don't want random HTML tags
showing up, but in these cases, we still want user names to be displayed
as text.

That worked okay as long as there was no "site=..." in there; this
change makes us able to handle site=... (basically we ignore it, but
then pick out the user name to display as text)
Merge pull request #318 from afuna/username-in-icon-browser-bug4868

(Bug 4868) Display the name even for external site tags