Comment 0 for bug 120005

When a developer wants to include a comment in a page template, that cannot be seen by viewing the HTML source of the resulting page, the current way of doing it is
    <tal:whatever condition="nothing">
      Comment goes here.
    </tal:whatever>

This has a high ratio of comment syntax to comment text. It would be nice if I could do something as compact as
    <!>Comment goes here.</!>

This could be achieved in any of several ways:
* adding it to upstream TAL;
* adding it to our own TAL tree;
* switching to a different template language that has a more compact comment syntax.