Added doc.

theano/gof/fg.py

@@ -574,6 +574,11 @@ class FunctionGraph(utils.object2):
 
         This is used primarily by the destroy_handler feature to ensure that all
         clients of any destroyed inputs have already computed their outputs.
+
+        :note: This only call the orderings() fct on all features. It don't take
+               care of computation dependencies by itself.
+               Do the DestroyHandler take orderings() fct take care of this?
+
         """
         ords = {}
         for feature in self._features: