Subclasses of CNetworkJob handle this by overriding shutdown().
This patch implements it for CHttpJob by simply tearing down the
underlying socket.
We also automatically call shutdown() after the job finishes,
regardless of success or failure. :^)
Now there's just CHttpRequest::set_url(URL), no need to specify the
host, port and path manually anymore.
Updated ChanViewer and Downloader for the API change.
