* plugins/fn-date/plugin.xml.in: Added function ISOYEAR.

* plugins/fn-date/functions.c (gnumeric_date, datedif_opt_yd, datedif_opt_md,
gnumeric_year, gnumeric_month, gnumeric_day, gnumeric_weekday,
gnumeric_days360, gnumeric_eomonth, gnumeric_workday, get_serial_weekday,
 networkdays_holiday_callback, gnumeric_networkdays): Replaced deprecated
g_date_xxx with g_data_get_xxx.
(gnumeric_isoweeknum): Cross reference ISOYEAR in docs.
(gnumeric_isoyear): New function implementing new spreadsheet funtion
ISOYEAR: The year an ISO 8601 week number refers to.

* plugins/fn-financial/functions.c (annual_year_basis, days_monthly_basis,
 coupnum): Replaced deprecated g_date_xxx with g_data_get_xxx.

* src/datetime.c (date_init, datetime_g_to_serial,
datetime_g_days_between, datetime_g_months_between, datetime_isoweeknum,
datetime_weeknum, days_between_BASIS_MSRB_30_360,
days_between_BASIS_30E_360, days_between_BASIS_30Ep_360,
days_between_basis, coup_cd): Ditto

* src/sheet-autofill.c (autofill_compute_delta): Ditto.