Installs virtualenv even when running in a Python version (e.g., 3.5) that supports pyvenv

[ut-adamc]

The Unix version of virtualenvwrapper works with pyvenv and does not install virtualenv. I don't really understand why the same approach couldn't work for virtualenvwrapper-win? (In fact, if I subsequently run pip uninstall virtualenv, virtualenvwrapper-win appears to keep working as expected.)

[utek]

Will take a look at this when I'll get myself some time :)