* Set VIRTUAL_ENV enviroment in activate_this.py

VIRTUAL_ENV was not set in activate_this.py, while set in other activate scripts.

* Add tests for activate_this.py

* Fix syntax in test_activate_this.py

* fix

* more robust testing for the activate this

* fix Jython support of activate this

- global variables capital
- pep-8 compliant variable names
- some pycharm specific ignores
- fixed some typos
- prefer format over %

* Always store _OLD_VIRTUAL_PATH in a sh compat format

When using a subshell from fish while within a virtualenv the
_OLD_VIRTUAL_PATH variable ends up in fish format and not the format of
the subshell. This breaks the first step of the activate script where it
attepts to deactivate the previous environment.

This patch will handle conversion to and from sh and fish formats within
the activate.fish script

* Add test and update to new delimiter

* Fix lint

Remove line that didn't lint as we don't need it.

* Rebuild virtualenv.py

* Add changelog

* fix_lint

* Try to add fish to build env

* Use less fish (only when running py tests)

* remove code duplication for activation testers

* Consolidate activation testing

- add tests for csh, bash
- rework bash, csh tests
- remove powershell singing
- powershell pydoc support

* file and with extension

* universal newline

* Add debug env var, and normalize on Linux to via realpath (Jython failure)

* switch to bat

* fix xonosh

* fix xonsh further

* fix jython

* fix lint

* enable pytest debug

This simplifies the code; it's still covered by the test I added for #956.

Thanks to @lilydjwg for the suggestion!

copyfile was broken for symlinks that pointed to relative paths, and for
symlinks that pointed to further symlinks (which meant that virtualenv
failed to work in some cases when the Python executable it found was
a symlink, e.g. when Python had been installed using stow or homebrew;
issue #268).

Make it follow symlinks until it finds an actual file to copy.

See https://github.com/pypa/pip/blob/master/src/pip/_vendor/README.rst

It is acceptable to remove the pip/_vendor/requests/cacert.pem file from pip

Virtualenv now doesn't error on that

fixes #1248

The previous value always resulted in a 404.

PS1 was set as undeclared (like when using shell provisionning in vagrant)

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_This was automatically migrated from pypa/virtualenv#893 to reparent it to the `master` branch. Please see original pull request for any previous discussion._

_Original Submitter: @allan-simon_