> Before we start pointing fingers or throwing mud, was this bug 
> fix which apparently breaking setuptools introduced knowing that 
> this would break setuptools users?
>
> I'm surprised that nobody at all tried to use the release candidate 
> with any of the listed packages.

The final release of 2.6.3 was done very shortly after the rc, so 
the community didn't have enough time to test their package with 
the rc.

What should have been done to avoid this (what what was suggested) is to
have a special buildbot for this that would run distutils commands over
a list of packages from the community.

I have a buidbot myself that does this, but it was discontinued lately 
because of a lack of CPU/Bandwidth.

> How hard would it be to release a 2.6.4 which differs from 2.6.3 
> only by not breaking existing setuptools distros?

I could work on this by making a special internal case in Distutils to
avoid calling the patched API that leads to the setuptools bug. This is
not hard and can be done quickly if required.