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/Capabilities/LLSDStreamHandler.cs

@@ -45,7 +45,7 @@ namespace OpenSim.Framework.Capabilities
         }
 
         public override byte[] Handle(string path, Stream request,
-                                      OSHttpRequest httpRequest, OSHttpResponse httpResponse)
+                                      IOSHttpRequest httpRequest, IOSHttpResponse httpResponse)
         {
             //Encoding encoding = Util.UTF8;
             //StreamReader streamReader = new StreamReader(request, false);