[osis-core] One more round on osisID/osisRef!

[Harry Plantinga]

> Do we really want to allow osisID (who am I) the ability to change the
> work they are claiming to be at a per tag level?  Maybe better as an
> attribute of osisText?

I agree that the normal situation would be for a document to use osisIDs
from a single standard. E.g. a document could declare itself to be a
"bible.lxx" and use only osisIDs like Matt.1.3.  However, might it
be possible that a document would contain a selection from Matthew
in Greek and in an English translation?

I.e. we have to decide if we want to allow "foreign" osisIDs, saying,
essentially,
"I am a chunk of the a text identified by the externally-defined
osisID standard called "bible.lxx"."

-Harry