Add ``--with-wheel-pkg-dir=PATH`` option to the ``./configure`` script. If
specified, the :mod:`ensurepip` module looks for ``setuptools`` and ``pip``
wheel packages in this directory: if both are present, these wheel packages are
used instead of ensurepip bundled wheel packages.

Some Linux distribution packaging policies recommend against bundling
dependencies. For example, Fedora installs wheel packages in the
``/usr/share/python-wheels/`` directory and don't install the
``ensurepip._bundled`` package.
