Re: Frontend error logging style

I wrote:
> Hmm, interesting. Taking up my point #2, I'd been thinking about
> proposing that we convert
> pg_log_error("query failed: %s", PQerrorMessage(conn));
> pg_log_error("query was: %s", todo);
> to
> pg_log_error("query failed: %s", PQerrorMessage(conn));
> pg_log_error_detail("Query was: %s", todo);

After looking around a bit, I see that a lot of these add-on messages
are more nearly hints than details, so we'd probably better support
both those cases right off the bat.

To move things along a bit, here's a draft patch to logging.h/.c only
to implement what I'm envisioning. I don't think there's much point
in doing the per-call-site gruntwork until we have agreement on what
the API is, so this seems like enough for discussion.

(As a fervent hater of colorization, I don't have an opinion about
whether or how to colorize the "detail:" and "hint:" fragments.
But I'll happily take somebody else's adjustment to add that.)

regards, tom lane