Calculates the number of days between two dates based on a 360-day year
(twelve 30-day months), which is used in some accounting calculations. Use
this function to help compute payments if your accounting system is based on
twelve 30-day months.
args - the evaluated function arguments. Empty values are represented with
BlankEval or MissingArgEval, never null.
srcRowIndex - row index of the cell containing the formula under evaluation
srcColumnIndex - column index of the cell containing the formula under evaluation
The evaluated result, possibly an ErrorEval, never null.
Note - Excel uses the error code #NUM! instead of IEEE NaN, so when
numeric functions evaluate to Double.NaN be sure to translate the result to ErrorEval.NUM_ERROR.