Combined redundant __(X)_AMOUNT__ and __TOTAL_(X)__ variables

We were tallying __TOTAL_DEBIT__ and __TOTAL_CREDIT__ but not using them,
and instead using the less clearly named __DEBIT_AMOUNT__ and
__CREDIT_AMOUNT__ parameters. Now we just use __FILE_TOTAL_DEBIT__ and
__FILE_TOTAL_CREDIT__. I have also removed the unnecessary batch variable
initialization in the constructor.

make_file_control_record will now complain if the total debits and total
credits do not match, leaving some balance unaccounted for. I updated the
sample records so they won't trigger this error.