Implement IOSHttpRequest and IOSHttpResponse http interfaces and use instead of OSHttpRequest/OSHttpResponse.

This is required for the substitution of different HTTP servers or the newer HttpServer.dll without having to commit to a particular implementation.
This is also required to write regression tests that involve the HTTP layer.
If you need to recompile, all you need to do is replace OSHttpRequest/OSHttpResponse references with IOSHttpRequest/IOSHttpResponse.

OpenSim/Server/Handlers/Authorization/AuthorizationServerPostHandler.cs

@@ -55,7 +55,7 @@ namespace OpenSim.Server.Handlers.Authorization
         }
 
         public override byte[] Handle(string path, Stream request,
-                OSHttpRequest httpRequest, OSHttpResponse httpResponse)
+                IOSHttpRequest httpRequest, IOSHttpResponse httpResponse)
         {
             XmlSerializer xs = new XmlSerializer(typeof (AuthorizationRequest));
             AuthorizationRequest Authorization = (AuthorizationRequest) xs.Deserialize(request);