Added sorting of working set used by zc.recipe.egg

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Install wheels via setuptools, fixes #425

Remove no longer existing winbot

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Fixed: could not install eggs with case issues

Setuptools 38.2.0 suddenly started supporting and downloading wheels.
.whl files would end up in the non-functioning and deprecated unpack_wheel().
The new default ('just use setuptools') works fine.

- If you use an older setuptools, setuptools won't download wheels and the new
  code won't be used.

- If you use buildout.wheel, you'll overwrite the unpacker anyway.

For instance when sdist file name and package name had different case.

Update implicit-parts.rst

miss {

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Use HTTPS for default PyPI index

PyPI redirects HTTP to HTTPS by default now so using HTTPS directly
avoids the potential for that redirect being modified in flight,
helping prevent MITM attacks.

Fixes #114.

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Egg `zope.testing` is already a dependency of `zc.buildout[test]`.

Add missing egg `coverage` to part that imports coverage on
initialization.

Fix #153: buildout should cache working set environments

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