Support multiple endpoints per socket

Sent messages will be scheduled among the endpoints according to socket
type: PUB will send the same data to all endpoints simultaneously, PUSH
will do round robin transfer.
Incoming data is fair queued between endpoints.

This is a feature of at least zeromq and nanomsg.

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To use: in the device configuration, instead of specifying just one address,
specify a comma separated list e.g.

tcp://localhost:123,ipc:///tmp/socket

the connection method (bind/connect) applies to all endpoints in this case.
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Mixing binding and connecting endpoints is supported:
prefix "@" means "bind", "+" (or ">") means connect, e.g.

+tcp://localhost:123,@ipc:///tmp/socket,ipc:///tmp/asd

(in case of missing prefix, the default channel method is used for that
endpoint).

fairmq/FairMQDevice.h

@@ -400,6 +400,16 @@ class FairMQDevice : public FairMQStateMachine, public FairMQConfigurable
     /// Connects a single channel (used in InitWrapper)
     bool ConnectChannel(FairMQChannel& ch);
 
+    /// Sets up and connects/binds a socket to an endpoint
+    /// return a string with the actual endpoint if it happens
+    //to stray from default.
+    bool ConnectEndpoint(FairMQSocket& socket, std::string& endpoint);
+    bool BindEndpoint(FairMQSocket& socket, std::string& endpoint);
+    /// Attaches the channel to all listed endpoints
+    /// the list is comma separated; the default method (bind/connect) is used.
+    /// to override default: prepend "@" to bind, "+" or ">" to connect endpoint.
+    bool AttachChannel(FairMQChannel& ch);
+
     /// Signal handler
     void SignalHandler(int signal);
     bool fCatchingSignals;