pgsql: Add a defense to prevent storing pseudo-type data into index

Log Message:
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Add a defense to prevent storing pseudo-type data into index columns.
Formerly, the lack of any opclasses that could accept such data was enough
of a defense, but now with a "record" opclass we need to check more carefully.
(You can still use that opclass for an index, but you have to store a named
composite type not an anonymous one.)

Modified Files:
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    pgsql/src/backend/catalog:
        index.c (r1.305 -> r1.306)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/index.c?r1=1.305&r2=1.306)