pgsql: Dept of second thoughts: seems it'd be safer if pg_typeof is

Log Message:
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Dept of second thoughts: seems it'd be safer if pg_typeof is marked
stable not immutable, since it depends on system catalog contents.

Modified Files:
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pgsql/src/include/catalog:
pg_proc.h (r1.522 -> r1.523)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.522&r2=1.523)