urlgrabber: Update to version v4.0.0


2019-02-25 Neal Gompa <ngompa13@gmail.com>

	* Port to Python 3
	* Add curl_obj option to grabber
	* Throw an obvious error message when urlgrabber-ext-down
	  is missing when attempting to use external downloader
	* Use setuptools for setup.py instead of distutils
	* bump version to 4.0.0

