Fix adding functions to CommandChainDispatcher with equal priority on Python 3.

Closes gh-1916

IPython/core/hooks.py

@@ -41,7 +41,8 b' somewhere in your configuration files or ipython command line.'
 #  the file COPYING, distributed as part of this software.
 #*****************************************************************************
 
-import os, bisect
+import os
+import operator
 import subprocess
 import sys
 
@@ -146,7 +147,8 b' class CommandChainDispatcher:'
 
     def add(self, func, priority=0):
         """ Add a func to the cmd chain with given priority """
-        bisect.insort(self.chain,(priority,func))
+        self.chain.append((priority, func))
+        self.chain.sort(key=operator.itemgetter(0))
 
     def __iter__(self):
         """ Return all objects in chain.

IPython/core/tests/test_hooks.py

@@ -73,3 +73,9 b' def test_command_chain_dispatcher_fofo():'
     nt.assert_true(okay1.called)
     nt.assert_false(fail2.called)
     nt.assert_false(okay2.called)
+
+def test_command_chain_dispatcher_eq_priority():
+    okay1 = Okay(u'okay1')
+    okay2 = Okay(u'okay2')
+    dp = CommandChainDispatcher([(1, okay1)])
+    dp.add(okay2, 1)