* Backports ensurepip to the 2.7 branch
* Backports some of the improved documentation to the 2.7 branch.
* Adds a private backport of the 3.x mock library as test._mock_backport
to enable saner testing of ensurepip.
Key Differences from 3.x:
* Ensurepip does not have any Makefile integration, specifically
it is not ran by default in the Makefile.
* There is no venv module in 2.7, so downstream distributors can
completely disable ensurepip, ideally with a message redirecting
to the correct way to install pip.
* To match the ``python`` command in 2.7, ensurepip will install
the unversioned ``pip`` command as well.
* No-op and hide --default-pip and add --no-default-pip to restore
the 3.x behavor on 2.7.
Donald Stufft
Benjamin Peterson
Victor Stinner
Georg Brandl