preparing 2.4.7 switched to the latest xmllint manual page from John

* configure.in: preparing 2.4.7
* Makefile.am doc/Makefile.am: switched to the latest xmllint
  manual page from John
* doc/*: updated the doc and rebuilt the generated pages
Daniel
diff --git a/doc/tree.html b/doc/tree.html
index f84e328..7fd0d77 100644
--- a/doc/tree.html
+++ b/doc/tree.html
@@ -49,6 +49,7 @@
 <li><a href="entities.html">Entities or no entities</a></li>
 <li><a href="namespaces.html">Namespaces</a></li>
 <li><a href="upgrade.html">Upgrading 1.x code</a></li>
+<li><a href="threads.html">Thread safety</a></li>
 <li><a href="DOM.html">DOM Principles</a></li>
 <li><a href="example.html">A real example</a></li>
 <li><a href="contribs.html">Contributions</a></li>