client: add task name and tweak postponed message

Makes it easier to see which task had problems when reading logs afterwards. Also include back off time in notice and drop fractional seconds.

client/app_control.cpp

@@ -390,12 +390,12 @@ void ACTIVE_TASK::handle_temporary_exit(
     } else {
         if (is_notice) {
             msg_printf(result->project, MSG_USER_ALERT,
-                "Task postponed: %s", reason
+                "Task %s postponed for %.f seconds: %s", result->name, backoff, reason
             );
         } else {
             if (log_flags.task) {
                 msg_printf(result->project, MSG_INFO,
-                    "task postponed %f sec: %s", backoff, reason
+                    "Task %s postponed for %.f seconds: %s", result->name, backoff, reason
                 );
             }
         }