reserve #,@ prefix for internal proc id and topic.

lichao

2021-05-21 11f6c600e55ca5677f93624efe44d2605cdd908d

 src/exported_symbols

@@ -5,6 +5,7 @@
   BHUnregister;
   BHRegisterTopics;
   BHQueryTopicAddress;
   BHQueryProcs;
   BHSubscribeTopics;
   BHStartWorker;
   BHHeartbeatEasy;