Identifiers should not be 'unique' per-collection.

Noticed this while running in production and tried to have different identifier keys per namespace.
My bad. :)
NOTE: If you're using the framework, grab the freshest copy and 
REMOVE all indexes from your collections, then run the script 
again and let the framework create its own indexes.
If the indexes aren't created (i.e. if the identifiers won't show up in your logs),
then create the indexes yourself!
e.g. run db.<NAMESPACE>.ensureIndex({date:1, metadata.<IDENTIFIER>:1});

over and out