Cause '*' and 'foo.*' notations to mark the referenced RTE(s) as

Cause '*' and 'foo.*' notations to mark the referenced RTE(s) as
requiring read permissions.  Up till now there was no possible case
in which the RTEs wouldn't already have ACL_SELECT set ... but now that
you can say something like 'INSERT INTO foo ... RETURNING *' this is
an essential step.  With this commit, a RETURNING clause adds the
requirement for SELECT permissions on the target table if and only if
the clause actually reads the value of at least one target-table column.