toProxy option is broken

Created by: samcday

In the first place it's somewhat poorly documented, so perhaps I'm just doing it wrong.

Say I do this:

  req.url = "http://destination/yay";

  proxy.web(req, res, {
    target: "http://mysquidproxy:3128",
    toProxy: true
  });

I should expect squidproxy:3128 to receive a GET http://destination/yay HTTP/1.1. Instead, it receives a GET http:/destination/yay HTTP/1.1 - note the single slash after protocol. It looks like common.urlJoin is causing the munging here.