zmq_socket(3) and zmq_setsockopt(3) man pages improved

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

doc/zmq_setsockopt.txt

@@ -12,7 +12,8 @@ SYNOPSIS
 --------
 *int zmq_setsockopt (void '*socket', int 'option_name', const void '*option_value', size_t 'option_len');*
 
-Caution: All options, with the exception of subscription strings, only take effect for subsequent socket bind/connects.
+Caution: All options, with the exception of ZMQ_SUBSCRIBE, ZMQ_UNSUBSCRIBE and
+ZMQ_LINGER, only take effect for subsequent socket bind/connects.
 
 DESCRIPTION
 -----------

doc/zmq_socket.txt

@@ -93,7 +93,8 @@ A socket of type 'ZMQ_REP' is used by a _service_ to receive requests from and
 send replies to a _client_. This socket type allows only an alternating
 sequence of _zmq_recv(request)_ and subsequent _zmq_send(reply)_ calls. Each
 request received is fair-queued from among all _clients_, and each reply sent
-is routed to the _client_ that issued the last request.
+is routed to the _client_ that issued the last request. If the original
+requester doesn't exist any more the reply is silently discarded.
 
 When a 'ZMQ_REP' socket enters an exceptional state due to having reached the
 high water mark for a _client_, then any replies sent to the _client_ in
@@ -143,7 +144,8 @@ prepend a message part containing the _identity_ of the originating peer to the
 message before passing it to the application. Messages received are fair-queued
 from among all connected peers. When sending messages a 'ZMQ_XREP' socket shall
 remove the first part of the message and use it to determine the _identity_ of
-the peer the message shall be routed to.
+the peer the message shall be routed to. If the peer does not exist anymore
+the message shall be silently discarded.
 
 When a 'ZMQ_XREP' socket enters an exceptional state due to having reached the
 high water mark for all peers, or if there are no peers at all, then any
@@ -210,7 +212,7 @@ Direction:: Unidirectional
 Send/receive pattern:: Receive only
 Incoming routing strategy:: Fair-queued
 Outgoing routing strategy:: N/A
-ZMQ_HWM option action:: N/A
+ZMQ_HWM option action:: Drop
 
 
 Pipeline pattern