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/Region/OptionalModules/World/WorldView/WorldViewRequestHandler.cs

@@ -56,7 +56,7 @@ namespace OpenSim.Region.OptionalModules.World.WorldView
         }
 
         public override byte[] Handle(string path, Stream requestData,
-                OSHttpRequest httpRequest, OSHttpResponse httpResponse)
+                IOSHttpRequest httpRequest, IOSHttpResponse httpResponse)
         {
             httpResponse.ContentType = "image/jpeg";