Add ZeroMQ support. Notify blocks and transactions via ZeroMQ

Continues Johnathan Corgan's work.
Publishing multipart messages

Bugfix: Add missing zmq header includes

Bugfix: Adjust build system to link ZeroMQ code for Qt binaries

src/zmq/zmqpublishnotifier.h

@@ -0,0 +1,41 @@
+// Copyright (c) 2015 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_ZMQ_ZMQPUBLISHNOTIFIER_H
+#define BITCOIN_ZMQ_ZMQPUBLISHNOTIFIER_H
+
+#include "zmqabstractnotifier.h"
+
+class CZMQAbstractPublishNotifier : public CZMQAbstractNotifier
+{
+public:
+    bool Initialize(void *pcontext);
+    void Shutdown();
+};
+
+class CZMQPublishHashBlockNotifier : public CZMQAbstractPublishNotifier
+{
+public:
+    bool NotifyBlock(const uint256 &hash);
+};
+
+class CZMQPublishHashTransactionNotifier : public CZMQAbstractPublishNotifier
+{
+public:
+    bool NotifyTransaction(const CTransaction &transaction);
+};
+
+class CZMQPublishRawBlockNotifier : public CZMQAbstractPublishNotifier
+{
+public:
+    bool NotifyBlock(const uint256 &hash);
+};
+
+class CZMQPublishRawTransactionNotifier : public CZMQAbstractPublishNotifier
+{
+public:
+    bool NotifyTransaction(const CTransaction &transaction);
+};
+
+#endif // BITCOIN_ZMQ_ZMQPUBLISHNOTIFIER_H