Adding comments to help understand psql hidden queries

The use of the --echo-hidden flag in psql is used to show people the way
psql performs its magic for its backslash commands. None of them has more
magic than "\d relation", but it suffers from needing a lot of separate
queries to gather all of the information it needs. Unfortunately, those
queries can get overwhelming and hard to figure out which one does what,
especially for those not already very familiar with the system catalogs.
Attached is a patch to add a small SQL comment to the top of each SELECT
query inside describeOneTableDetail. All other functions use a single
query, and thus need no additional context. But "\d mytable" has the
potential to run over a dozen SQL queries! The new format looks like this:

/******** QUERY *********/
/* Get information about row-level policies */
SELECT pol.polname, pol.polpermissive,
CASE WHEN pol.polroles = '{0}' THEN NULL ELSE
pg_catalog.array_to_string(array(select rolname from pg_catalog.pg_roles
where oid = any (pol.polroles) order by 1),',') END,
pg_catalog.pg_get_expr(pol.polqual, pol.polrelid),
pg_catalog.pg_get_expr(pol.polwithcheck, pol.polrelid),
CASE pol.polcmd
WHEN 'r' THEN 'SELECT'
WHEN 'a' THEN 'INSERT'
WHEN 'w' THEN 'UPDATE'
WHEN 'd' THEN 'DELETE'
END AS cmd
FROM pg_catalog.pg_policy pol
WHERE pol.polrelid = '134384' ORDER BY 1;
/************************/

Cheers,
Greg