We want two identical sections at different URL to be able to produce
same signature. This is feature is useful for slapos.recipe.cmmi's
shared parts.

Rebase instructions:
- squash with "apply "Support ${:_profile_base_location_}."

If we use options.items() we visit all keys and not used options cannot
be detected.

Rebase instructions:
- squash with "Add referred parts' hash strings in
  __buildout_signature__, that invokes rebuild of a part
  when one of its (recursive) dependencies are modified"
- add a comment explaining why such a lower level API is used

The version of Python should not affect the behaviour of a recipe.
Anyway, it was already ignored for DEVELOP_DIST eggs.

This makes the slapos mechanism to share parts more efficient. And with
the upcoming changes in buildout & slapos.recipe.cmmi, there would be
no way for the slapos.reboostrap extension to prevent everything from
being rebuilt when reboostrapping to a different version of Python,
if bootstrap parts are shared.

The monkey-patch by slapos.reboostrap now becomes useless.

Add referred parts' hash strings in __buildout_signature__,
that invokes rebuild of a part when one of its (recursive)
dependencies are modified.

Also remove duplicates and sort entries in __buildout_signature__.

Squashed with fixup!:

The purpose is to make the part signature available sooner,
during recipe's __init__.

Original commit already broke detection of unused options in sections.

Squashed with:

Chomp ../ from beginging of filenames

In order to have as canonical as possible paths,
chomp ../ from filenames and recalculate base.

Squashed with:

fixup! Support ${:_profile_base_location_}

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.

[ci skip]

[skip ci]

[ci skip]

[ci skip]

[skip ci]

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

[skip ci]

[skip ci]

in 3.11

Also update action/checkout version