pgsql: Fix cash_mul_int4 and cash_div_int4 for overenthusiastic

Log Message:
-----------
Fix cash_mul_int4 and cash_div_int4 for overenthusiastic substitution
of int64 for int32.  Per reports from Merlin Moncure and Andrew Chernow.

Modified Files:
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    pgsql/src/backend/utils/adt:
        cash.c (r1.72 -> r1.73)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/cash.c?r1=1.72&r2=1.73)