attempt to suppress exceptions in daemon threads at shutdown

clean shutdown could result in Attribute/TypeErrors in channel
threads due to garbage collection of namespaces.  Now
try to ignore these exceptions if the shutdown process is detected.

IPython/zmq/kernelmanager.py

@@ -16,6 +16,7 b' TODO'
 #-----------------------------------------------------------------------------
 
 # Standard library imports.
+import atexit
 import errno
 import json
 from subprocess import Popen
@@ -91,6 +92,7 b' class ZMQSocketChannel(Thread):'
     ioloop = None
     stream = None
     _address = None
+    _exiting = False
 
     def __init__(self, context, session, address):
         """Create a channel
@@ -113,6 +115,10 b' class ZMQSocketChannel(Thread):'
             message = 'The port number for a channel cannot be 0.'
             raise InvalidPortNumber(message)
         self._address = address
+        atexit.register(self._notice_exit)
+    
+    def _notice_exit(self):
+        self._exiting = True
 
     def _run_loop(self):
         """Run my loop, ignoring EINTR events in the poller"""
@@ -124,6 +130,11 b' class ZMQSocketChannel(Thread):'
                     continue
                 else:
                     raise
+            except Exception:
+                if self._exiting:
+                    break
+                else:
+                    raise
             else:
                 break
 
@@ -517,6 +528,11 b' class HBSocketChannel(ZMQSocketChannel):'
                     pass
                 else:
                     raise
+            except Exception:
+                if self._exiting:
+                    break
+                else:
+                    raise
             else:
                 break
         return events