Need ability to modify multiple datastores simultaneously

[dcamper]

It is often the case that multiple datasets (flat files or indexes) need to be promoted/demoted together. If a failure to promote or demote occurs with one set of data, none of the related sets of data should be modified.

In the context of DataMgmt, there needs to be a method to 'stage' updates to a set of datastores and then (nearly) atomically update or promote all changes at once. Tactically, this could be implemented as a specific 'staging' superfile that collects update and serves as a "gen-0" pool that lives outside of the normal generational data management flow. Actions on data in the staging area would be only: replacing, appending, clearing, and promoting.

Other use cases involve explicit promoting/demoting data between generations across multiple datastores.