Plock

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- Support mutually exclusive options ``plock .`` and ``plock -l``
- Restore preserve add-ons functionality and make it default

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- Create install_dir if it does not exist
- Use Plock Pins instead of PythonPackages as zc.buildout configuration host
- Add -v, ``--version`` to display version
- Bug fix: don't break ``--list-addons``
- Bug fix: don't break ``--install-addons``
- Remove ``--insecure``
- Remove ``--virtualenv``
- Remove ``--zope2-only``

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- Bug fix: Buildout command execution

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- Bug Fix: Buildout command execution

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- Add ``--expert`` command line argument, does same thing as PLOCK_EXPERT environment variable
- Add ``--insecure`` command line argument to allow extending remote hosted configuration files
- Bug fix: prevent inadvertently switching from Plone to Zope2 or vice versa
- Bug fix: configure Buildout command relative to current working directory, instead of relying on source bin/activate

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- Add experimental feature ``--zope2-only`` option to install Zope2 only.
- Bug fix: exit Plock when egg count remains the same for longer than or equal to PLOCK_TIMEOUT