Added upsertBatch that delivers the records updated with auto-incremented key

Hi Jens, I am with GreatVines in Portland, USA. We used IDBWrapper to create a mock implementation of the Salesforce SmartStore (a database component in the Salesforce Mobile SDK). Since SmartStore returns the records upon completion of an upsert operation, we added a new method to IDBStore called upsertBatch. Optionally you can request this method to update a field in the record to contain the auto-generated key. We decided on a new method instead of enhancing putBatch since putBatch returns a true/false result instead of the records.  Maybe this new method could be added to IDBWrapper.

Peter