Re: Disabling vacuum truncate for autovacuum

We added isset_offset to the public struct to introduce this new general behavior of tracking whether any table reloption has been set (not just vacuum_truncate) without any comments.

I get the need for this kind of logic, since we used a boolean for the table option, but as a self-proclaimed hack it seems worth more comments than provided here.  Especially pertaining to whether this is indeed generic or vacuum_truncate specific.  It's unclear since both isset and vacuum_truncate_set have been introduced.  If it is now a general property applying to any setting then vacuum_truncate_set shouldn't be needed - we should just get the isset value of the existing vacuum_truncate reloption by name.

David J.