pgsql: Dept of second thoughts: the IQ of estimate_array_length() needs

Log Message:
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Dept of second thoughts: the IQ of estimate_array_length() needs to be
kept on par with that of scalararraysel(), else estimates that should
track might not.  Hence teach it about binary-compatible cases, too.

Modified Files:
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    pgsql/src/backend/utils/adt:
        selfuncs.c (r1.222 -> r1.223)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c.diff?r1=1.222&r2=1.223)