This partially implements the LSL function to set the response

type for an HTTP request. Since the "official" LSL function limits
the use of the response type, it is implemented as osSetContentType
with a string for the content mime type and a threat level of high.
With this function you should be able to implement rather functional
media-on-a-prim application with much less difficulty.

OpenSim/Region/Framework/Interfaces/IUrlModule.cs

@@ -39,6 +39,8 @@ namespace OpenSim.Region.Framework.Interfaces
         UUID RequestSecureURL(IScriptModule engine, SceneObjectPart host, UUID itemID);
         void ReleaseURL(string url);
         void HttpResponse(UUID request, int status, string body);
+        void HttpContentType(UUID request, string type);
+        
         string GetHttpHeader(UUID request, string header);
         int GetFreeUrls();