[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/DefinitionCacheFactory.php

@@ -20,7 +20,7 @@ class HTMLPurifier_DefinitionCacheFactory
     /**
      * Retrieves an instance of global definition cache factory.
      */
-    public static function &instance($prototype = null) {
+    public static function instance($prototype = null) {
         static $instance;
         if ($prototype !== null) {
             $instance = $prototype;
@@ -45,7 +45,7 @@ class HTMLPurifier_DefinitionCacheFactory
      * @param $name Name of definitions handled by cache
      * @param $config Instance of HTMLPurifier_Config
      */
-    public function &create($type, $config) {
+    public function create($type, $config) {
         $method = $config->get('Cache', 'DefinitionImpl');
         if ($method === null) {
             $null = new HTMLPurifier_DefinitionCache_Null($type);