add content_type attribute to MSRPChatGotMessage notification

darcs-hash:20090227113428-b2873-ce31fe6feb8dc7ac828351620f3b8aef55d80e6f
MSRPChat: port DidEnd instead of DidFail if the connection was closed cleanly

darcs-hash:20090227133056-b2873-5064fe5c88be6b2e8888cbb1713a420d6d790a9c