Pip-run

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29: Unconditionally honor ``.pth`` files in installed
packages.

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28: Avoid error when arguments to ``pip install``
existed but did not indicate any packages to install.

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Added support for Jython by using JYTHONPATH instead
of PYTHONPATH when on Jython.

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Use ``io.open`` in ``scripts`` reader for better Jython
compatibility. See `Jython 2696
<http://bugs.jython.org/issue2696>`_ for more info.

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Dropped support for injecting modules to sys.path when
Setuptools is older than 19.6.2 (presumed unused).

Package now uses Setuptools declarative config and thus
will not install from sdist without Setuptools 30.3 or later.

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Added support for pip 10, including addressing 25. As a
side benefit, warnings are no longer issued when no
requirements are supplied.