In Vector main.php, look for
<!-- start footer -->
It is at the bottom of the file. You will find:
<li id="footer-info-lastmod">
<?php tpl_pageinfo()?><br />
</li>
Replace:
<?php tpl_pageinfo()?><br />
with:
<?php
$pinfo=tpl_pageinfo(true);
list($page,$rest)=explode('·',$pinfo);
$page = str_replace('.txt',"",$page);
$page = str_replace('/',':',$page);
$url = DOKU_URL."doku.php?id=$page";
echo "<a href='$url'>$url</a>" . ' ·' . $rest;
?><br />