Revising nsIChannel to allow for overlapped i/o. This consists of three parts:

1. Factoring nsIChannel into a protocol specific part, the nsIChannel, and a socket specific, the nsITransport.
2. Derive the nsIChannel from a nsIRequest.
2. Changes the notification system from necko and the URILoader to pass the nsIRequest interface instead of nsIChannel interface.

This goal stems from wanting to be able to have active AsyncRead and AsyncWrite operations on nsSocketTransport.
This is desired because it would greatly simplify the task of maintaining persistent/reusable socket connections
for FTP, HTTP, and Imap (and potentially other protocols).  The problem with the existing nsIChannel interface is
that it does not allow one to selectively suspend just one of the read or write operations while keeping the other active.

The full details of the change on written up in the netlib newsgroup.

r=darin@netscape.com
sr=rpotts@netscape.com

docshell/base/nsDocShell.h

@@ -191,9 +191,9 @@ protected:
    NS_IMETHOD EnsureDeviceContext();
    NS_IMETHOD CreateAboutBlankContentViewer();
    NS_IMETHOD CreateContentViewer(const char* aContentType, 
-      nsIChannel* aOpenedChannel, nsIStreamListener** aContentHandler);
+      nsIRequest *request, nsIStreamListener** aContentHandler);
    NS_IMETHOD NewContentViewerObj(const char* aContentType, 
-      nsIChannel* aOpenedChannel, nsILoadGroup* aLoadGroup, 
+      nsIRequest *request, nsILoadGroup* aLoadGroup, 
       nsIStreamListener** aContentHandler, nsIContentViewer** aViewer);
    NS_IMETHOD SetupNewViewer(nsIContentViewer* aNewViewer);