pgsql: Fix cash_in() to behave properly in locales where frac_digits is

Log Message:
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Fix cash_in() to behave properly in locales where frac_digits is zero,
eg Japan.  Report and fix by Itagaki Takahiro.  Also fix CASHDEBUG printout
format for branches with 64-bit money type, and some minor comment cleanup.

Back-patch to 7.4, because it's broken all the way back.

Tags:
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REL8_3_STABLE

Modified Files:
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    pgsql/src/backend/utils/adt:
        cash.c (r1.77.2.1 -> r1.77.2.2)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/cash.c?r1=1.77.2.1&r2=1.77.2.2)