Fix cash_in() to behave properly in locales where frac_digits is zero,

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.