detects and uses proxies based on the environment variables. If the proxy
  was given as an explicit option it worked, but due to the setup order
  mistake proxies would not be used fine for a few protocols when picked up
  from '[protocol]_proxy'. Obviously this broke after 7.19.4. I now also added
  test case 1106 that verifies this functionality.

  (http://curl.haxx.se/bug/view.cgi?id=2913886)