Re: BUG #16419: wrong parsing BC year in to_date() function

I wrote:
> I think this is nuts. The current behavior is obviously broken;
> we should just treat it as a bug and fix it, including back-patching.
> I do not think there is a compatibility problem of any significance.
> Who out there is going to have an application that is relying on the
> ability to insert BC dates in this way?

Concretely, I propose the attached. This adjusts Dar Alathar-Yemen's
patch (it didn't do the right thing IMO for the combination of bc
and year < 0) and adds test cases and docs.

Oracle would have us throw an error for year zero, but our historical
behavior has been to read it as 1 BC. That's not so obviously wrong
that I'd want to change it in the back branches. Maybe it could be
done as a follow-up change in HEAD.

regards, tom lane