Added short-cuts methods in Message_Messenger for sending message with specified gravity,
and stream buffer class for using stream-like interface for that.
Similar short-cuts to DefaultMessenger() are added in Message package.
ViewerTest has been updated to send messages to Message::DefaultMessenger()
instead of direct output to std::cout/std::cerr.
Off-topic: spelling error (duplicate "and") is corrected in two places
Added test bugs fclasses bug31189
23fe70ec52