redirectURL is null for 301 redirects with relative Location header

[JalfResi]

1. Which version of PhantomJS are you using? Tip: run phantomjs --version.
   2.1.1
2. What steps will reproduce the problem?
   1. Visit a url which redirects, in which the url responding with 301 has a relative location header
   2. The resource.redirectURL is set to null in the onResourceReceived callback handler
3. Which operating system are you using?
   OSX El Capitan
4. Did you use binary PhantomJS or did you compile it from source?
   Binary
5. Please provide any additional information below.

[JalfResi]

Phantom should resolve the relative URLs in the location header to absolute urls, and then set the redirectURL property of the resource.

[stale]

Due to our very limited maintenance capacity, we need to prioritize our development focus on other tasks. Therefore, this issue will be automatically closed (see #15395 for more details). In the future, if we see the need to attend to this issue again, then it will be reopened. Thank you for your contribution!