[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/AttrDef/HTML/ID.php

@@ -66,7 +66,7 @@ class HTMLPurifier_AttrDef_HTML_ID extends HTMLPurifier_AttrDef
     // ref functionality disabled, since we also have to verify
     // whether or not the ID it refers to exists
     
-    public function validate($id, $config, &$context) {
+    public function validate($id, $config, $context) {
         
         if (!$config->get('Attr', 'EnableID')) return false;