pgsql: Doc: caution against misuse of 'now' and related datetime litera
Doc: caution against misuse of 'now' and related datetime literals.
Section 188.8.131.52, which defines these literals, made only a vague
reference to the fact that they might be evaluated too soon to be
safe in non-interactive contexts. Provide a more explicit caution
against misuse. Also, generalize the wording in the related tip in
section 9.9.4: while it clearly described this problem, it implied
(or really, stated outright) that the problem only applies to table
Per gripe from Tijs van Dam. Back-patch to all supported branches.