When generating an environment dict for subprocess calls to pip,
os.environ was accidentally modified despite efforts to copy it
and modify only the copy, as copy.copy(os.environ) is not enough.

When looking up a distribution to install an egg, keep strictly to
the provided index-url and find-links and do not use distributions
that are already on sys.path.

This change was introduced because of a situation where installing
an egg failed due to a bad distribution somehow available inside a
virtual environment. Could not remember how to reproduce.

By default egg installation considers the path where buildout
and other build tools such as setuptools are installed to see
if the requested eggs are already installed there.

With the new bootstrapping behavior, bootstrap should install
buildout and the other build tools in the local egg directory
even if the pinned versions are already installed in sys.path.

With this mode zc.buildout and its dependencies are installed
from scratch directly in the local eggs directory, following
the pinned versions if any apply.

In offline mode this merely ensures that the required eggs are
already installed in the local eggs and develop-eggs directory.

The previous behavior is still available by passing a non-empty
set of arguments to bootstrap, e.g. bootstrap --old-behavior.

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For example: `[versions:python_version <= "3.9"]`.
Fixes https://github.com/buildout/buildout/issues/621

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in 3.11

Also update action/checkout version

files in subdirs were not managed

in the dev environment

Also fixed virtualenv install under 2.7

* Make compatible with pip 22.2+, restoring Requires-Python functionality there.

Fixes https://github.com/buildout/buildout/issues/613.

Note: we are patching `process_url` from `setuptools`.
The existing comment says that this method was copied over from setuptools 46.1.3.
I was wondering, so I checked: the method is still the same in latest setuptools.  And it is largely unchanged since setuptools 42.0.2.
So for that part we should still be compatible with quite a long range of setuptools versions.

* process_url patch: must pass cache_link_parsing=False.

This fixes test failures: extdemo-1.5 was not found, because the previous index page containing only extdemo-1.4 was cached.
We were passing this before to HTMLPage, and still do as a fallback, but I missed that this was also needed in pip 22.2+ for the new IndexContent class.

Add support for python311-315 in conditional section expressions. [master]