add link to doxygen.log

[[Imported from SVN: r846]]

doc/doxygen/doxy-footer.html

@@ -5,6 +5,7 @@
 <p class="foot">
   Generated on $date with <a
   href="http://www.doxygen.org/">Doxygen</a> (ver $doxygenversion)  
+  [<a href="doxygen.log">logfile</a>].
 </p>
 
 </div>