override form_build_context instead of form_render so we get sure to call...

override form_build_context instead of form_render so we get sure to call form_add_entity_hiddens even on subforms

--HG--
branch : tls-sprint

web/form.py

@@ -358,9 +358,9 @@ class EntityFieldsForm(FieldsForm):
                 msg = '%s %s' % (msg, self.req._('and linked'))
             self.form_add_hidden('__message', msg)
         
-    def form_render(self, **values):
+    def form_build_context(self, values):
         self.form_add_entity_hiddens(self.edited_entity.e_schema)
-        return super(EntityFieldsForm, self).form_render(**values)
+        return super(EntityFieldsForm, self).form_build_context(values)
 
     def form_add_entity_hiddens(self, eschema):
         for field in self.fields[:]: