socket handling should not raise exception

```
    notifier.loop()
  File "/usr/lib/pymodules/python2.7/notifier/nf_generic.py", line 283, in loop
    step()
  File "/usr/lib/pymodules/python2.7/notifier/nf_generic.py", line 258, in step
    sock_obj = __sock_objects[ fd ]
KeyError: 14
```
