Built zmq_send_const man page properly

doc/Makefile.am

@@ -3,7 +3,7 @@ MAN3 = zmq_bind.3 zmq_unbind.3 zmq_connect.3 zmq_disconnect.3 zmq_close.3 \
     zmq_msg_init.3 zmq_msg_init_data.3 zmq_msg_init_size.3 \
     zmq_msg_move.3 zmq_msg_copy.3 zmq_msg_size.3 zmq_msg_data.3 zmq_msg_close.3 \
     zmq_msg_send.3 zmq_msg_recv.3 \
-    zmq_send.3 zmq_recv.3 \
+    zmq_send.3 zmq_recv.3 zmq_send_const.3 \
     zmq_msg_get.3 zmq_msg_set.3 zmq_msg_more.3 \
     zmq_getsockopt.3 zmq_setsockopt.3 \
     zmq_socket.3 zmq_socket_monitor.3 zmq_poll.3 \

doc/zmq.txt

@@ -140,6 +140,7 @@ Sending and receiving messages::
     linkzmq:zmq_msg_recv[3]
     linkzmq:zmq_send[3]
     linkzmq:zmq_recv[3]
+    linkzmq:zmq_send_const[3]
 
 .Input/output multiplexing
 0MQ provides a mechanism for applications to multiplex input/output events over

doc/zmq_send_const.txt

 zmq_send_const(3)
-===========
+=================
 
 
 NAME