add support to node-mongodb-native v1.4

Mongodb native 1.4+ fixes an issue with $not and keys that start with $, for example:

```js
collection.remove({name: { $not: { $in: ['Bob', 'Steve' 'Larry' ] } } })
```

You can see more about the issue [here](https://github.com/LearnBoost/mongoose/issues/2012).

This adds support for Mongodb native 1.4.2. It's a little hacky because of `mongodb.Admin` now extends `this` directly (instead of the prototype). This hack just copies everything over. It doesn't change how anything else is implemented.

All tests are passing on my machine with mongodb 2.6.

Cheers!