[Distutils] Differences in PEP386 and setuptools

[Daniel Holth]

This is the worst bikeshed topic. I would like to keep PEP-386 as much
as possible, only because the time-consuming agreement has already
happened.

For wheel I had to add an alphanumeric build number apart from the
main version because you need to be able to distinguish e.g. a RHEL
build from a Debian build just by including a string like RedHat's 1fc
or 1el build numbers.