Clean up stray exceptions following broker disconnect with TLS (#51)

Python 3.4 started raising ValueError instead of AttributeError when writing to
a disconnected SSL socket. When the client writes some stray messages following
a call to disconnect(), they are not caught in Python 3.4 or Python 3.5.
Signed-off-by: NJason Swails <jason.swails@gmail.com>

src/paho/mqtt/client.py

@@ -1325,10 +1325,10 @@ class Client(object):
         Messages that match 'sub' will be passed to 'callback'. Any
         non-matching messages will be passed to the default on_message
         callback.
-        
+
         Call multiple times with different 'sub' to define multiple topic
         specific callbacks.
-        
+
         Topic specific callbacks may be removed with
         message_callback_remove()."""
         if callback is None or sub is None:
@@ -1501,7 +1501,7 @@ class Client(object):
                     write_length = self._ssl.write(packet['packet'][packet['pos']:])
                 else:
                     write_length = self._sock.send(packet['packet'][packet['pos']:])
-            except AttributeError:
+            except (AttributeError, ValueError):
                 self._current_out_packet_mutex.release()
                 return MQTT_ERR_SUCCESS
             except socket.error as err:
@@ -2340,7 +2340,7 @@ class Client(object):
         raise ssl.SSLError('Certificate subject does not match remote hostname.')
 
 
-# Compatibility class for easy porting from mosquitto.py. 
+# Compatibility class for easy porting from mosquitto.py.
 class Mosquitto(Client):
     def __init__(self, client_id="", clean_session=True, userdata=None):
         super(Mosquitto, self).__init__(client_id, clean_session, userdata)