number of application threads to use 0MQ sockets is unlimited; app_threads parameter in zmq_init is unused and obsolete

src/config.hpp

@@ -27,6 +27,10 @@ namespace zmq
 
     enum 
     {
+        //  Maximal number of OS threads that can own 0MQ sockets
+        //  at the same time.
+        max_app_threads = 512,
+
         //  Number of new messages in message pipe needed to trigger new memory
         //  allocation. Setting this parameter to 256 decreases the impact of
         //  memory allocation by approximately 99.6%