No real time to respond in detail here, but one small comment.
I see some responses to that post which indicate that the specific bug will be fixed, and that's good, but there is definitely a pattern he's talking about here, not just one issue. I think there is a general pattern of small, difficult to detect breakages in Python.
Remember these words...
For example, did anyone here know that the new-style exceptions stuff in 2.5 caused hundreds of unit-test failures in Twisted? I am glad the change was made, and one of our users did catch it, so the process isn't fatally broken, but it is still worrying.
When implementing this stuff, I could have merely made it possible for exceptions to be new-style, and left the builtin exceptions as classic classes. This didn't seem to be an especially good idea, as it would leave code working _most_ of the time, only to break horribly when confronted with a rare new-style exception. So I made the decision (and I don't think I ever got around to explicitly discussing this with anyone, nor if the people who actually updated my patch and checked it in thought about it at all) to make the built in exceptions new-style, precisely to make it a screamingly obvious change. I didn't _know_ when I was doing it that I'd break Twisted unit tests, but I was hardly a surprise.
I think the idea of a buildbot running various projects tests suites with svn HEAD is a great idea -- back when I was doing 2.2.1 I did run a few third party test suites (zodb comes to mind) but as always with these things, automation is a good idea.