[update to 16.3.0] Copy only required files from exec_prefix and only…

… if it is really different from prefix path (#1282)

Adam Sampson (2):
      Dereference symlinks more thoroughly in copyfile (#956)
      Use os.path.realpath to resolve the symlink. (#1259)

Anthony Scopatz (1):
      Xonsh Support (#1206)

Anthony Sottile (3):
      Update outdated docs referring to bin/rebuild-script.py (#1286)
      Use importlib over imp in python3.x (#1289)
      produce a virtualenv zipapp (#1287)

Antti Haapala (1):
      Allow sourcing activate.sh in shells "exit on error" mode

Bernat Gabor (19):
      fix master not embeded
      pass through proxy and HOME variables
      add ISSUE/PR template, include pyproject.toml, clean not needed news
      Add news documenation for #1244
      clarify project
      add changelog
      Move to a declarative build script via setup.cfg, improve package metadata
      add pytest xdist to speed up tests
      add release Azure task
      fix releae
      release 16.2.0
      fish 3 compatbility
      also deploy sdist
      fix linting
      add stale issue
      try to fix brew CI break
      fix documentation, alter faulty examples
      avoid packaging non source code
      release 16.3.0

Bernát Gábor (11):
      enable test report for forks (#1243)
      bump embeded wheels (#1257)
      Shell fixes (#1258)
      code improvements (#1262)
      Jython enable for coverage report. (#1263)
      revert to a non src layout (#1264)
      Fix boostrap script generation (#1265)
      Support the embed script on Windows (#1266)
      make assertions on packaging, recommend tox for all testings (#1267)
      as powershell is now universaly available, do not enforce Windows line endings (#1268)
      bump vendored pip to 19.0.1 (#1291)

BrownTruck (1):
      solved problem when using -u in a non interactive shell (#922)

George Lund (1):
      Link to Python 3 venv

Jurko Gospodnetić (1):
      update testing notes, and test space path support

Kyle Altendorf (1):
      Discourage installation as root, such as with sudo (#1283)

Mickaël Schoentgen (1):
      Fix ResourceWarning: unclosed file (#1277)

Microdog (1):
      Pre-import some built-in modules in PyPy (#1281)

Miro Hrončok (2):
      Add test for missing pip/certifi's cacert.pem
      Fix error with missing pip/certifi's cacert.pem

Sviatoslav Sydorenko (1):
      Fix testenv:upgrade deps in tox config (#1276)

Wouter De Borger (1):
      made lib64 symlink relative again (#1249)

Zachary Ware (1):
      Update default license URL to match upstream (#1247)

anatoly techtonik (1):
      Document when --always-copy was introduced (in PR #409)

daa (2):
      Do not override certificate bundle if it is defined in pip config (#1273)
      Copy only required files from exec_prefix and only if it is really different from prefix path (#1282)

drevicko (1):
      added instructions for changing --system-site-packages in existing envir... (#738)

nonylene (1):
      Set VIRTUAL_ENV enviroment variable in activate_this.py (#1057)

ptaneli (1):
      Move to news files for changelog via towncrier. (#1234)

ykdojo (1):
      Fixed a typo in index.rst (#1269)

Éric Araujo (1):
      fix reporting in site module (#1245)

v16.3.0 (2019-01-25)
--------------------

Bugfixes
^^^^^^^^

- Use ``importlib`` over deprecated ``imp` in ``distutils/__init__.py`` for python 3 - by Anthony Sottile (`#955 <https://github.com/pypa/virtualenv/issues/955>`_)
- Preserve ``cert`` option defined in ``pip.conf`` or environment variable. (`#1273 <https://github.com/pypa/virtualenv/issues/1273>`_)
- fixed a ``ResourceWarning: unclosed file`` in ``call_subprocess()`` - by Mickaël Schoentgen (`#1277 <https://github.com/pypa/virtualenv/issues/1277>`_)
- pre-import some built-in modules in ``site.py`` on PyPy according to PyPy's ``site.py`` - by microdog (`#1281 <https://github.com/pypa/virtualenv/issues/1281>`_)
- Copy files from ``sys.exec_prefix`` only if it is really different path than
  used prefix, bugfix for #1270 (`#1282 <https://github.com/pypa/virtualenv/issues/1282>`_)

Features

(NEWS truncated at 15 lines)