Thanks John -- I had some time now and used your code to factor the
_handle_message code into a separate class. This avoids recomputing
values and in particular the parameter-passing. Otherwise this is quite
identical to your refactoring.
I had to fix the bugs mentioned earlier, added some more tests for
things that were not covered (message id generation) and have also fixed
the parameter parsing (-C and -S options) to work with other classes not
named "issue" (hopefully, for this there is no test yet).

Fixed in r4577