Add the directories in `dirs` to the `sys.path`.  A venv.pth file
        will be written in the site-packages dir of this virtualenv to add
        dirs to sys.path.

        dirs: a list of directories.

def venv_pth(self, dirs):
        '''
        Add the directories in `dirs` to the `sys.path`.  A venv.pth file
        will be written in the site-packages dir of this virtualenv to add
        dirs to sys.path.

        dirs: a list of directories.
        '''
        # Create venv.pth to add dirs to sys.path when using the virtualenv.
        text = StringIO.StringIO()
        text.write("# Autogenerated file.  Do not modify.\n")
        for path in dirs:
            text.write('{}\n'.format(path))
        put(text, os.path.join(self.site_packages_dir(), 'venv.pth'), mode=0664)