* cal-backend.h: moved CalendarFormat type def here
* cal-backend.c (cal_backend_load): if extension suggests
an ical file, attempt to load an iCal file.
(cal_get_type_from_filename): returns CAL_ICAL if file
extension is 'ics' or 'ifb', else returns CAL_VCAL
(icalendar_calendar_load): moved this here from
icalendar.c because it needs to call the static function
add_object.
svn path=/trunk/; revision=1831
4cd07c4e96