add note about potential bug in verticals. No time to investigate at the moment...

common/lib/xmodule/xmodule/vertical_module.py

@@ -48,3 +48,5 @@ class VerticalDescriptor(SequenceDescriptor):
     js = {'coffee': [resource_string(__name__, 'js/src/vertical/edit.coffee')]}
     js_module_name = "VerticalDescriptor"
         
+    # TODO (victor): Does this need its own definition_to_xml method?  Otherwise it looks
+    # like verticals will get exported as sequentials...