Add conversion functions for our own tree format.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

library/HTMLPurifier/Token/Comment.php

@@ -29,6 +29,10 @@ class HTMLPurifier_Token_Comment extends HTMLPurifier_Token
         $this->line = $line;
         $this->col = $col;
     }
+
+    public function toNode() {
+        return new HTMLPurifier_Node_Comment($this->data, $this->line, $this->col);
+    }
 }
 
 // vim: et sw=4 sts=4