Add flushing to stdout/stderr in system calls.

IPython/zmq/zmqshell.py

@@ -1,20 +1,22 b''
 import sys
 from subprocess import Popen, PIPE
 from IPython.core.interactiveshell import InteractiveShell, InteractiveShellABC
 
 
 class ZMQInteractiveShell(InteractiveShell):
     """A subclass of InteractiveShell for ZMQ."""
 
     def system(self, cmd):
         cmd = self.var_expand(cmd, depth=2)
+        sys.stdout.flush()
+        sys.stderr.flush()
         p = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE)
         for line in p.stdout.read().split('\n'):
             if len(line) > 0:
                 print line
         for line in p.stderr.read().split('\n'):
             if len(line) > 0:
                 print line
         return p.wait()
 
 InteractiveShellABC.register(ZMQInteractiveShell)