When we render a page that contains a table of contents, the contents of
referenced files may have changed also and that will change how the
referenced file appears in the table of contents. So we must pass not only
a particular section to render but any blob content of modified referenced
pages.

Now that tables of contents do render, rewrite the links to those pages
to open up the correponding XML file in the editor.
handle dead citation links gracefully with an error message

When we render section previews, simple-2 generates dead links for
internal citations because we do not have an index file available
that maps section citations to their filename. It puts a call to
a Javascript function instead.

This commit implements that javascript function. Otherwise it would
log an error to the console about the function not being defined.