Backport PR #4118: ZMQ heartbeat channel: catch EINTR exceptions and continue.

The zmq heartbeat channel exits when it encounters an
"Interrupted system call", thereby causing the qtconsole to
report that it is not responding, despite the console working
perfectly fine. Observed in a large Qt application embedding
the ipython qtconsole in KDE desktop.
Fixes  #2310
Inspired by  #501

IPython/kernel/zmq/heartbeat.py

@@ -1,56 +1,65
 """The client and server for a basic ping-pong style heartbeat.
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
+import errno
 import os
 import socket
 from threading import Thread
 
 import zmq
 
 from IPython.utils.localinterfaces import LOCALHOST
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 
 class Heartbeat(Thread):
     "A simple ping-pong style heartbeat that runs in a thread."
 
     def __init__(self, context, addr=('tcp', LOCALHOST, 0)):
         Thread.__init__(self)
         self.context = context
         self.transport, self.ip, self.port = addr
         if self.port == 0:
             if addr[0] == 'tcp':
                 s = socket.socket()
                 # '*' means all interfaces to 0MQ, which is '' to socket.socket
                 s.bind(('' if self.ip == '*' else self.ip, 0))
                 self.port = s.getsockname()[1]
                 s.close()
             elif addr[0] == 'ipc':
                 self.port = 1
                 while os.path.exists("%s-%s" % (self.ip, self.port)):
                     self.port = self.port + 1
             else:
                 raise ValueError("Unrecognized zmq transport: %s" % addr[0])
         self.addr = (self.ip, self.port)
         self.daemon = True
 
     def run(self):
         self.socket = self.context.socket(zmq.REP)
         c = ':' if self.transport == 'tcp' else '-'
         self.socket.bind('%s://%s' % (self.transport, self.ip) + c + str(self.port))
-        zmq.device(zmq.FORWARDER, self.socket, self.socket)
-
+        while True:
+            try:
+                zmq.device(zmq.FORWARDER, self.socket, self.socket)
+            except zmq.ZMQError as e:
+                if e.errno == errno.EINTR:
+                    continue
+                else:
+                    raise
+            else:
+                break