[3.1.0] More PHP4->PHP5 conversions, notably reference removal of most methods that return objects

- Removed HTMLPurifier_Error
- Documentation updates
- Removed more copy() methods in favor of clone
- HTMLPurifier::getInstance() to HTMLPurifier::instance()
- Fix InterchangeBuilder to use HTMLPURIFIER_PREFIX

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1689 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/LanguageFactory.php

@@ -53,7 +53,7 @@ class HTMLPurifier_LanguageFactory
      * @param $prototype Optional prototype to overload sole instance with,
      *                   or bool true to reset to default factory.
      */
-    public static function &instance($prototype = null) {
+    public static function instance($prototype = null) {
         static $instance = null;
         if ($prototype !== null) {
             $instance = $prototype;