[Nitro] composite primary key

[TRANS]

How does one set the a user-defined primary key now? It should be as
simple as setting that to to an array of keys instead of a singe key.
And the rest should be automatic. I imagine that'll require some
simple improvements to the SQL generation code to take multiple keys
into account.

Sorry, I can't be more specific but I'm still too busy with other
things at the moment (i.e. Facets) to devel into Og any deeper.

T.