Download cufflinks GTF files

def get_cufflinks():
    "Download cufflinks GTF files"
    for size, md5, url in cufflinks:
        cuff_gtf = os.path.join(args.data_dir, os.path.basename(url))
        if not _up_to_date(md5, cuff_gtf):
            download(url, cuff_gtf)