title: Don't download an existing file with axel
body: <p>I have an script that reads some urls and get them to axel to download them. I want stop script on sometimes and resume it further. Axel can resumes file downloading. So if I press Ctrl+C when downloading, the next time, it starts from the resume of file.</p>
  
  <p>but axel doesn't check that the file existed. So it appends ".0" to the end of file name and start downloding it twice. How I can tell to axel if the file with same name existed, skip that and don't downloading it??</p>