bcoe/karait — Issue #6: request atomic write()
Author: ZoomQuiet
Created: 2011-11-30 10:19:40+00:00
State: open

thanx for the simple and pythonic MQ base MongoDB;
- commonly, karait had to accept multi-message-sender
- so, duplicate message always happened
- so, we realy need the karait.write() lilke as $upset :
- point unique key
- if there is't same message, write into new
- else there is same message, cancel write, retuen None

hope result as:
```python
queue.write({'pid':123, 'action': 'wget ...'},
unique='pid')
```
this feature should append karait?