Maxmin support #4359: patch for http_proxy authorization

Here are some changes I made to libGeoIP  so I could get through an HTTP proxy that required a username and password.  This was support ticket #4359 when I first asked if you wanted the patch, but that was so long ago, I suspect the ticket is long since been closed.  Anyway, when I saw you had the code here, I figured I'd just go ahead and submit a pull request.  Enjoy.