flush outgoing heartbeats

Prevents mismatch between heartbeat timer and actual heartbeat send/recv events.

Applied in notebook and parallel.

IPython/frontend/html/notebook/handlers.py

@@ -481,6 +481,8 b' class IOPubHandler(AuthenticatedZMQStreamHandler):'
                 if self._kernel_alive:
                     self._kernel_alive = False
                     self.hb_stream.send(b'ping')
+                    # flush stream to force immediate socket send
+                    self.hb_stream.flush()
                 else:
                     try:
                         callback()

IPython/parallel/controller/heartmonitor.py

@@ -124,6 +124,8 b' class HeartMonitor(LoggingConfigurable):'
         # print self.on_probation, self.hearts
         # self.log.debug("heartbeat::beat %.3f, %i beating hearts", self.lifetime, len(self.hearts))
         self.pingstream.send(asbytes(str(self.lifetime)))
+        # flush stream to force immediate socket send
+        self.pingstream.flush()
 
     def handle_new_heart(self, heart):
         if self._new_handlers: