MSRPChat: better and consistent attributes for MSRPChatDidDeliver and DidNotDeliver

darcs-hash:20090227100307-b2873-8adb5ef440abeb8a0a631ae5e80cb49b796b2ae7
MSRPChat: for MSRPChatDidFail notification data rename 'reason' to 'failure'

darcs-hash:20090227101141-b2873-b3b577744108bb2449a6454fa37f93201dcac9d4