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

contrib/zmq/zmq_sub.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python2
+
+import array
+import binascii
+import zmq
+
+port = 28332
+
+zmqContext = zmq.Context()
+zmqSubSocket = zmqContext.socket(zmq.SUB)
+zmqSubSocket.setsockopt(zmq.SUBSCRIBE, "hashblock")
+zmqSubSocket.setsockopt(zmq.SUBSCRIBE, "hashtx")
+zmqSubSocket.setsockopt(zmq.SUBSCRIBE, "rawblock")
+zmqSubSocket.setsockopt(zmq.SUBSCRIBE, "rawtx")
+zmqSubSocket.connect("tcp://127.0.0.1:%i" % port)
+
+try:
+    while True:
+        msg = zmqSubSocket.recv_multipart()
+        topic = str(msg[0])
+        body = msg[1]
+
+        if topic == "hashblock":
+            print "- HASH BLOCK -"
+            print binascii.hexlify(body)
+        elif topic == "hashtx":
+            print '- HASH TX -'
+            print binascii.hexlify(body)
+        elif topic == "rawblock":
+            print "- RAW BLOCK HEADER -"
+            print binascii.hexlify(body[:80])
+        elif topic == "rawtx":
+            print '- RAW TX -'
+            print binascii.hexlify(body)
+
+except KeyboardInterrupt:
+    zmqContext.destroy()