* 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

* 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

The newly added `pydoc` unaliasing command ends with exit code 1 if `pydoc` alias is not set; this in turn means that sourcing `activate.sh` in a shell that had been set to exit on first error, upon sourcing that file, will exit on that line. And thanks to suppressing the output of `pydoc` there is no error message being displayed. Simply adding `|| true` should ensure that the command ends successfully.

The previous value always resulted in a 404.

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

---

_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_

* initial version of xonsh activate

* partially add activate.xsh to virtualenv.py

* Add base64-encoded xonsh script

* actiavte.xsh

* some initial tests

* fixed deactivate argument error

* added source command to xonsh test and added newline to the end of activate.xsh

* remove powershell refs

* add xonsh to testing requirements

* black tests/activation/test_xonsh_activation.py

* need raw string to escape paths in windows

* some path safety fixes

* put in some debug for tests

* black the test

* change import order

* added docs

* @gaborbernat feedback

* better python version constratints for xonsh

* black

* xonsh install version includes minor

* refactor need_xonsh

* removed unused import

* removed blank line

Thanks to a new ``sys.__interactivehook__`` on Python 3.

* Added activate.ps1 to list of generated activation scripts
* extended tests to cover cmdline
* Use path_locations to test directories
* Add tests for powershell activation
* Fix environment creation for cmdline tests
* pwsh.exe on Windows
* make executable dependent tests optional locally
* fixes
* fix path normalization and casing
* turn path to long
* debug
* fix documentation

Universal newlines are deprecated as of python3.5, which makes the
following warning be emitted when deprecation warnings are enabled:

  .tox/py35/lib/python3.5/site.py:165: DeprecationWarning: 'U' mode is deprecated