[3.0.0] Convert all $context calls away from references

- Update TODO list
- URISchemeRegistry doesn't return a reference for instance anymore, should do the same for other singletons

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1477 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/HTMLModule/Scripting.php

@@ -12,7 +12,7 @@ INSIDE HTML PURIFIER DOCUMENTS. USE ONLY WITH TRUSTED USER INPUT!!!
  */
 class HTMLPurifier_AttrTransform_ScriptRequired extends HTMLPurifier_AttrTransform
 {
-    public function transform($attr, $config, &$context) {
+    public function transform($attr, $config, $context) {
         if (!isset($attr['type'])) {
             $attr['type'] = 'text/javascript';
         }