On Python 3, response.msg.keys() contains the same value multiple times if
there are multiple headers with the same value. Work around this by
converting to a set before iterating over it.
Let's not use Google to test redirects since it changes depending on your
geographic location. I changed the test to use httpbin.org, since
a lot of our tests already depend on httpbin.org anyway.
Somedays, I'd like to implement my own local mock HTTP server I
can do asserts against. The test suite would just start it up,
and the server would record the requests, which I could then
retrieve and compare.
Closes#21
