Minor buildfarm HOWTO comment

BTW, I noticed that the buildfarm HOWTO says

> ... Finally, I set up a
> cron job on the mirror machine to update the mirror every 15 minutes - this
> should not be too big a deal, as CVSup is extremely efficient, and even
> doing this so frequently should not incur a lot of bandwidth use.

AFAIK the Postgres anonymous-CVS server is only updated from the master
once an hour, and so there is no point in CVSup'ing from it more than
once an hour.

If you are a committer with direct access to the master CVS server then
maybe there's some point in CVSup'ing your local copy every 15 minutes,
but I think the HOWTO shouldn't recommend that.

(CVS mirrors used only for buildfarm purposes should probably mirror the
slave CVS server anyway, even if you have access rights to the master
server, on grounds of security and bandwidth conservation ...)
        regards, tom lane