Revert "BASE_HREF's host part differs from HTTP_HOST (www prepended) causing issues in Opera 12"

This reverts commit 7ab7b50ac4.

include/header.inc

@@ -65,7 +65,9 @@ if (isset($shortname) && $shortname) {
  <script type="text/javascript" src="<?php echo $STATIC_ROOT ?>js/ext/html5.js"></script>
  <![endif]-->
 
- <base href="http://<?php echo $_SERVER["HTTP_HOST"] . $_SERVER["SCRIPT_NAME"] ?>">
+<?php if (!empty($_SERVER["BASE_HREF"])): ?>
+ <base href="<?php echo $_SERVER["BASE_HREF"] ?>">
+<?php endif ?>
 
 <?php
  $jsfiles = array('ext/modernizr.js');