* src/datetime.c (datetime_g_free): New function to free
GDate. Can be called with NULL without complaining.
(coupdays, coupdaybs, coupdaysnc):

* src/sheet-autofill.c (autofill_compute_delta, autofill_cell):
Use datetime_g_free instead of g_date_free.

* src/functions/fn-financial.c (days_monthly_basis, func_coup)
(gnumeric_accrint, gnumeric_price, gnumeric_yield)
(gnumeric_oddfprice): Use datetime_g_free instead of g_date_free.

* src/functions/fn-date.c (gnumeric_datedif, gnumeric_edate,
gnumeric_edate) (gnumeric_edate, gnumeric_days360, get_serial_weekday)
(networkdays_holiday_callback): Ditto.