Fix for #22 and #218

#22: Updated to scrapper.py to return the cli options when the _MOZDOWNLOADARGCOMPLETE is in environment. Added completion scripts for bash and zsh. Updates to setup.py for the new completion scripts.
#218: Updated nightly with candidates in scrapper.py (ReleaseCandidateScrapper::candidate_build_list_regex). Updates to tests.
So when you move the files from nightly/ to candidate/, you should use `git mv` instead of the plain `mv` command. See http://githowto.com/moving_files