Issue 22878: PEP 477 - "make install" and "make altinstall" integration

The backport of ensurepip to 2.7.9 allows pip to optionally be installed
or upgraded using the bundled pip provided by the new ensurepip module.
The option can be specified persistently using the configure option:

    ./configure --with-ensurepip[=upgrade|install|no]

It can also be overridden on either the "install" or "altinstall" targets:

    make [alt]install ENSUREPIP=[upgrade|install|no]

For Python 2, the default option is "no" (do not install pip).

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branch : 2.7
Issue #22827: Backport the new Distributing and Instaling Docs from 3.4

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branch : 2.7
Issue #21963: backout issue #1856 patch (avoid crashes and lockups when
daemon threads run while the interpreter is shutting down; instead,
these threads are now killed when they try to take the GIL), as it seems
to break some existing code.

--HG--
branch : 2.7
Add regression issue number to Misc/NEWS entry.

--HG--
branch : 2.7