updateAttributes on jugglingdb-redis breaks index for non-string fields

Thank you for all your hard work. I ran into an issue with the jugglingdb-redis adapter. I have several fields that are defined such as:

``` javascript
status: { type: Number, default: 1, index: true }
```

When I create an instance of the object with that field it saves fine and I can see in the store that there is an index created. However if I call updateAttributes on the same instance later the index actually disappears. I've debugged this and traced it back to the following code: [redis.js Line291](https://github.com/jugglingdb/redis-adapter/blob/master/lib/redis.js#L291). It compares the value being saved with the previous value and if they are different it adds the new one and removes the old one. The problem is it uses a !== for comparison so even though you could be passing the same value it will be removed if it is a number, or date or anything but a string. All keys and values in `prevData` are strings because they come from the hash that was retrieved with a `hgetall` at line 260. So when you try to do a `findOne` later on `status` it fails because it was removed from the index.

Let me know if this makes sense. I'd love to have this working so that I can use numbers, booleans, etc. and still search on them even after updating the records.