Change the visibility of getStream to public.

Because sometimes, we would like to access to the PHP resource. This was
protected for several “security” reasons but this is often blocking to
not being able to access the PHP resource directly.

Stream.php

@@ -347,7 +347,7 @@ public function getStreamName()
      *
      * @return  resource
      */
-    protected function getStream()
+    public function getStream()
     {
         if (empty($this->_bucket)) {
             return null;