Download setuptools from a specified location and return its filename

    `version` should be a valid setuptools version number that is available
    as an egg for download under the `download_base` URL (which should end
    with a '/'). `to_dir` is the directory where the egg will be downloaded.
    `delay` is the number of seconds to pause before an actual download
    attempt.

    ``downloader_factory`` should be a function taking no arguments and
    returning a function for downloading a URL to a target.

def download_setuptools(version=DEFAULT_VERSION, download_base=DEFAULT_URL,
                        to_dir=os.curdir, delay=15,
                        downloader_factory=get_best_downloader):
    """Download setuptools from a specified location and return its filename

    `version` should be a valid setuptools version number that is available
    as an egg for download under the `download_base` URL (which should end
    with a '/'). `to_dir` is the directory where the egg will be downloaded.
    `delay` is the number of seconds to pause before an actual download
    attempt.

    ``downloader_factory`` should be a function taking no arguments and
    returning a function for downloading a URL to a target.
    """
    # making sure we use the absolute path
    to_dir = os.path.abspath(to_dir)
    tgz_name = "setuptools-%s.tar.gz" % version
    url = download_base + tgz_name
    saveto = os.path.join(to_dir, tgz_name)
    if not os.path.exists(saveto):  # Avoid repeated downloads
        log.warn("Downloading %s", url)
        downloader = downloader_factory()
        downloader(url, saveto)
    return os.path.realpath(saveto)