Part of fix for bug 28348. Add Progress Dialog. R=varada, SR=sspitzer

mailnews/compose/src/nsMsgComposeStringBundle.h

@@ -103,5 +103,7 @@ private:
 
 /* 12554 is taken by NS_ERROR_NNTP_NO_CROSS_POSTING.  use 12555 as the next one */
 
+#define NS_MSG_CANCELLING                           NS_MSG_GENERATE_SUCCESS(12555)
+
 
 #endif /* _nsMsgComposeStringBundle_H_ */