[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/Language.php

@@ -36,7 +36,7 @@ class HTMLPurifier_Language
      */
     protected $config, $context;
     
-    public function __construct($config, &$context) {
+    public function __construct($config, $context) {
         $this->config  = $config;
         $this->context =& $context;
     }