pgsql: Fix the code that adds regclass constants to a plan's list of

Log Message:
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Fix the code that adds regclass constants to a plan's list of relation OIDs
that it depends on for replan-forcing purposes.  We need to consider plain OID
constants too, because eval_const_expressions folds a RelabelType atop a Const
to just a Const.  This change could result in OID values that aren't really
for tables getting added to the dependency list, but the worst-case
consequence would be occasional useless replans.  Per report from Gabriele
Messineo.

Tags:
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REL8_3_STABLE

Modified Files:
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    pgsql/src/backend/optimizer/plan:
        setrefs.c (r1.141 -> r1.141.2.1)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/setrefs.c?r1=1.141&r2=1.141.2.1)