[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/Lang.php

@@ -9,7 +9,7 @@ require_once 'HTMLPurifier/AttrDef.php';
 class HTMLPurifier_AttrDef_Lang extends HTMLPurifier_AttrDef
 {
     
-    public function validate($string, $config, &$context) {
+    public function validate($string, $config, $context) {
         
         $string = trim($string);
         if (!$string) return false;