Manypex

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* Upgrade to ``setuptools>=1``

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* ``twitter.common.python`` is no longer a namespace package

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* Kill the egg distiller. We now delegate .egg generation to bdist_egg.
`RB 55 <https://rbcommons.com/s/twitter/r/55/>`_

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* Short-circuit resolving a distribution if a local exact match is found.
`RB 47 <https://rbcommons.com/s/twitter/r/47/>`_

* Correctly patch the global ``pkg_resources`` ``WorkingSet`` for the lifetime
of the Python interpreter. `RB 52 <https://rbcommons.com/s/twitter/r/52/>`_

* Fixes a performance regression in setuptools ``build_zipmanifest``
`Setuptools Issue 154 <https://bitbucket.org/pypa/setuptools/issue/154/build_zipmanifest-results-should-be>`_
`RB 53 <https://rbcommons.com/s/twitter/r/53/>`_

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* Plumb through the ``--zip-safe``, ``--always-write-cache``, ``--ignore-errors``
and ``--inherit-path`` flags to the pex tool.

* Delete the unused ``PythonDirWrapper`` code.

* Split ``PEXEnvironment`` resolution into ``twitter.common.python.environment``
and deconflate ``WorkingSet``/``Environment`` state.

* Removes the monkeypatched zipimporter in favor of keeping all eggs
unzipped within PEX files. Refactors the PEX dependency cache in
``util.py``

* Adds interpreter detection for Jython and PyPy.

* Dependency translation errors should be made uniform.
(Patch from johnsirois)

* Adds ``PEX_PROFILE_ENTRIES`` to limit the number of entries reported when
``PEX_PROFILE`` is enabled. (Patch from rgs_)

* Bug fix: Several fixes to error handling in ``twitter.common.python.http``
(From Marc Abramowitz)

* Bug fix: PEX should not always assume that ``$PATH`` was available.
(Patch from jamesbroadhead)

* Bug fix: Filename should be part of the .pex cache key or else multiple
identical versions will incorrectly resolve (Patch from tc)

* Bug fix: Executed entry points shouldn't be forced to run in an
environment with ``__future__`` imports enabled. (Patch from
lawson_patrick)

* Bug fix: Detect versionless egg links and fail fast. (Patch from
johnsirois.)

* Bug fix: Handle setuptools>=2.1 correctly in the zipimport monkeypatch
(Patch from johnsirois.)

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* Bug fix: Fix handling of Fetchers with ``file://`` urls.