[Distutils] Changing the status of PEP 440 to Provisional

After an offline discussion with Donald regarding feedback on the setuptools 8.0 release, I'm proposing we change the status of PEP 440 to be Provisional (in the PEP 411 sense) until we sort out the additional issues that were revealed through actual adoption. I can't actually make that change to the PEP text itself yet (as PEP 1, and hence the PEP index generator, don't currently include the notion of provisional acceptance), but this is the basis on which we're proposing to make changes to the previously accepted PEP text (rather than creating a new PEP). I'll also be proposing the relevant changes to PEP 1 and the index generator to make this an official feature of the PEP process to python-dev. Cheers, Nick.