Don't bail on WindowsError which is not existing on non-windows systems.

Discussion see https://github.com/zopefoundation/Zope/commit/87c5992e7e40604df206bb713e42bafd5919fe64

- Allow buildout to pick versions using ranges which enable updates
  to third-dot releases in the same line as previous pins.

- Show the versions picked.

See:  https://bugs.launchpad.net/zope2/+bug/789863

This change applies Leo Rochael's patch from:
https://bugs.launchpad.net/zope2/+bug/789863/+attachment/3624368/+files/0001-Make-the-request-object-unpublishable.patch

And the ideas from Richard Mitchell's patch at:
https://bugs.launchpad.net/zope2/+bug/789863/+attachment/3625765/+files/request_object.patch

Also, add an assertion that the WSGIResponse gets its 'Content-Length'
header correctly set.

Conflicts:
	doc/CHANGES.rst

Addresses:
https://github.com/zopefoundation/Zope/pull/32/files#r32951940

[ci skip]

Document running under WSGI server.

Addresses:
https://github.com/zopefoundation/Zope/pull/32/files#r32919776

[ci skip]

[ci skip]

[ci skip]

- Add docs for installation into a virtualenv.
- Update Sphinx paths to use '_' prefix.

Closes #30.

- Products.BTreeFolder2:  2.13.5.

WSGI begin / end interaction fixes

Backporting WSGIPublisher interaction fixes.

Wrap in try-finally.

Cherry-pick c73dfcd1 from master.

Make it analogous to the ZServer publisher.

Cherry-pick 41594f6d from master.

- DateTime: 2.12.8
- zLOG: 2.11.1.

Note repos which need (but don't yet have) such release branches.

- Products.ExternalMethod -> 2.13.1

- Products.MailHost -> 2.13.2

- Products.StandardCacheManagers -> 2.13.1