[HACKERS] Inconsistencies between pg_settings and postgresql.conf

Hello, 

We are working with postgresql.conf configuration file and we have found some discrepancies between it and pg_settings in terms of categories and subcategories (we have split the field category in pg_settings by '/', the first part being 'category', the second 'subcategory')  

We suggest to change the postgresql.conf.sample file with the attached diff to resolve these inconsistencies. 

We think that these changes could also be backported to previous versions. 

Looking forward to your comments,