reserve #xxx proc id for internal use.

lichao

2021-05-21 1c92e4cbc85f9501660444cb76ebb06770da9376

 src/exported_symbols

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