demonstrate faulty sort by _id method

The sort method appears to be incorrectly translating an _id parameter to just "id" when it passes it to Mongo. 

If you tail the log/test.log file, you see the reference to "_id" being converted into just "id". Because none of the mongo documents have an actual "id" attribute, the documents are unsorted. 

I've tried this with both 0.13.0-beta1 and 0.13.0-beta2. It works correctly with 0.12.0.

This pull requests demonstrates the failure. 

Attention @cheald