explain more to user when VIRTUAL_ENV is set but PATH is wrong
attempted fix of windows totally disregarding PATH in Popen
version bump
use distutils.spawn.find_executable to resolve --python arg on win

vex isn't even processing the argument, so virtualenv itself is failing
here. This is a terrible workaround for the failures of Windows and
virtualenv to resolve arguments for convenience of Windows users.
Windows users should probably be used to specifying full paths to python
version bump