[development] multisite shared table upgrade enhancements (was what would be more useful)

[Karthik]

> the only solution that is even somewhat workable in my small brain is to
> warn the user and then upgrade all the sites at once. i think thats the
> deal with multi-site. you need to do separate sites if you want them to
> be on different versions. if you can think of more flexible solutions,
> thats great.

How about having:
a) a separate table for tracking table versions?

or

b) Using the System table to hold table versions under
"schema_versions" and type "table"? I've not really played with
multisites myself: Is the system table shared in certain scenarios?

or

c) using the comments field of each table to hold version information?
But I don't think this would be pgSQL friendly.

So each update block would check the table version, apply update and
update the table version upon completion. This would allow all sites
to be able to apply updates irrespective of whether any of the shared
tables have already been updated.

How do Bryght et al. handle this?

-K