pgsql: Allow implicit cast from any named composite type to RECORD.

Log Message:
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Allow implicit cast from any named composite type to RECORD.  At the
moment this has no particular use except to allow table rows to be
passed to record_out(), but that case seems to be useful in itself
per recent example from Elein.  Further down the road we could look
at letting PL functions be declared to accept RECORD parameters.

Modified Files:
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    pgsql/src/backend/parser:
        parse_coerce.c (r2.127 -> r2.128)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_coerce.c.diff?r1=2.127&r2=2.128)