pyenv-virtualenv 20140705

Changes:

* Display information on auto-(de)?activation
* Support manual (de)?activation with auto-activation enabled
* Exit as error when (de)?activation failed
* Use https://bootstrap.pypa.io/ to install setuptools and pip
* Create backup of original virtualenv within `$(pyenv root)/versions` when `--upgrade`

Closes #30669.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>