Ralf:

I just went through CHANGES.txt and

 issue2550826 - Capture some exceptions from auditors/reactors and
  raise a DetectorError instead.

 issue2550755 - exceptions.NotFound(msg) msg is not reported to user
  in cgi.

seem to touch exceptions directly:

 also I am not sure if:

  issue1408570 - Finally fix that form values are lost on edit
      exceptions.

may have changed something in the flow.

  Add RejectRaw exception to allow unescaped HTML error messages to be
  displayed to the user 

  Pythons cgi form code can return a TypeError, we now guard for this
  condition.

 also there were a bunch of changes to move from the:
    raise Exception, explanation to
    raise Exception(explanation)
and inherit from BaseException and not Exception for python 2 and 3 
support. This started at: 5248:bc16d91b7a50

maybe revert to bc16d91b7a50 and see if that is a quick fix

-- rouilj