Database api hole

[pavlis]

I uncovered an inconsistency in the Database class api. The update_metadata method does not support Metadata as arg1. That would surely surprise any user. It is not as easy to fix, as I first though, by adding Metadata to the isinstance test at the top of the function. The function has numerous instances of using the kill mechanism to tag data as bad from various failures.

That function is complicated enough I suggest we do this:

1. Change the name of update_metadata to update_data_attributes to not create the metadata confusion. We may even want to call it _update_data_attributes because it really should be treated as a private method because it probably should not be used by users.
2. Create a new method called save_metadata that does the much simpler operation of just insert_one of the contents of a Metadata container only. i.e. it only does the "C" operation in CRUD.

Another topic for today's conference call.