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/zmqabstractnotifier.cpp

@@ -0,0 +1,22 @@
+// 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.
+
+#include "zmqabstractnotifier.h"
+#include "util.h"
+
+
+CZMQAbstractNotifier::~CZMQAbstractNotifier()
+{
+    assert(!psocket);
+}
+
+bool CZMQAbstractNotifier::NotifyBlock(const uint256 &/*hash*/)
+{
+    return true;
+}
+
+bool CZMQAbstractNotifier::NotifyTransaction(const CTransaction &/*transaction*/)
+{
+    return true;
+}