Added warning that FancyURLopener prompts the user on the terminal when basic authentication is needed.
Added warning that FancyURLopener prompts the user on the terminal when
basic authentication is needed.

Added documentation for FancyURLopener.prompt_user_passwd(), explaining
that subclasses should provide more appropriate behavior for the hosting
environment.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator