Code review comment for lp:~jtv/launchpad/recife-552639

The tests in danilo's separate branch now pass. I've made a few design changes, fixed one or two mistakes in the code, and changed the expected behavior of a few tests. But for something this big, not bad.

The few relevant tests that are in this branch you can run with:
{{{
./bin/test -vv -t test_potmsgset
}}}

If you're not using the feature branch (lp:~launchpad/launchpad/recife) as a merge base you will see some failures from resetCurrentTranslation tests, which are unrelated to this code. Henning has already fixed those in the main feature branch.

I'm going to put up the test suite for separate review, in order to keep line count in check.