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/Map/MapGetServerConnector.cs

@@ -80,7 +80,7 @@ namespace OpenSim.Server.Handlers.MapImage
             m_MapService = service;
         }
 
-        public override byte[] Handle(string path, Stream request, OSHttpRequest httpRequest, OSHttpResponse httpResponse)
+        public override byte[] Handle(string path, Stream request, IOSHttpRequest httpRequest, IOSHttpResponse httpResponse)
         {
             byte[] result = new byte[0];