Added the connection argument to the parse_response method.

An edge case seems to still be missing a required argument to Redis.client parse_response method. This happens in the `_poll_error` method of kombu/transport/redis.py .  Obviously this only happens when there is an error to trigger to the call to` _poll_error`, which is probably the reason it has so far been unnoticed.  Also updated a unit test accordingly.  

Here's an example stack trace without the fix:
```
[2013-12-09 12:15:14,788: ERROR/MainProcess] Unrecoverable error: TypeError('parse_response() takes exactly 3 arguments (2 given)',)
Traceback (most recent call last):
  File "/opt/python2.7.1/lib/python2.7/site-packages/celery/worker/__init__.py", line 404, in start
    component.start()
  File "/opt/python2.7.1/lib/python2.7/site-packages/celery/worker/consumer.py", line 410, in start
    self.consume_messages()
  File "/opt/python2.7.1/lib/python2.7/site-packages/celery/worker/consumer.py", line 501, in consume_messages
    handlermap[fileno](fileno, event)
  File "/opt/python2.7.1/lib/python2.7/site-packages/kombu/transport/redis.py", line 763, in handle_event
    ret = self.cycle.handle_event(fileno, event)
  File "/opt/python2.7.1/lib/python2.7/site-packages/kombu/transport/redis.py", line 284, in handle_event
    chan._poll_error(type)
  File "/opt/python2.7.1/lib/python2.7/site-packages/kombu/transport/redis.py", line 499, in _poll_error
    self.client.parse_response(type)
TypeError: parse_response() takes exactly 3 arguments (2 given)
```

Here's an example stack trace with the first commit of the fix applied:
```
[2013-12-09 14:16:48,597: ERROR/MainProcess] Unrecoverable error: AttributeError("'NoneType' object has no attribute 'readline'",)
Traceback (most recent call last):
  File "/opt/python2.7.1/lib/python2.7/site-packages/celery/worker/__init__.py", line 404, in start
    component.start()
  File "/opt/python2.7.1/lib/python2.7/site-packages/celery/worker/consumer.py", line 410, in start
    self.consume_messages()
  File "/opt/python2.7.1/lib/python2.7/site-packages/celery/worker/consumer.py", line 501, in consume_messages
    handlermap[fileno](fileno, event)
  File "/opt/python2.7.1/lib/python2.7/site-packages/kombu/transport/redis.py", line 765, in handle_event
    ret = self.cycle.handle_event(fileno, event)
  File "/opt/python2.7.1/lib/python2.7/site-packages/kombu/transport/redis.py", line 284, in handle_event
    chan._poll_error(type)
  File "/opt/python2.7.1/lib/python2.7/site-packages/kombu/transport/redis.py", line 499, in _poll_error
    self.client.parse_response(self.client.connection, type)
  File "/opt/python2.7.1/lib/python2.7/site-packages/redis/client.py", line 370, in parse_response
    response = connection.read_response()
  File "/opt/python2.7.1/lib/python2.7/site-packages/redis/connection.py", line 304, in read_response
    response = self._parser.read_response()
  File "/opt/python2.7.1/lib/python2.7/site-packages/redis/connection.py", line 102, in read_response
    response = self.read()
  File "/opt/python2.7.1/lib/python2.7/site-packages/redis/connection.py", line 87, in read
    return self._fp.readline()[:-2]
AttributeError: 'NoneType' object has no attribute 'readline'
```

Here's an example from celery warning logs when the latest version of the fix is applied. 
```
WARNING/MainProcess] Unable to read from channel <kombu.transport.redis.Channel object at 0x2bcbf90> of type LISTEN. Err: 'NoneType' object has no attribute 'readline'
[2013-12-10 13:53:06,303: WARNING/MainProcess] (The event was 8)
```