#63 UNTIL of date type should define an inclusive bound

[an0]

According to rfc 2445:
"The UNTIL rule part defines a date-time value which bounds the recurrence rule in an inclusive manner. If the value specified by UNTIL is synchronized with the specified recurrence, this date or date-time becomes the last instance of the recurrence."

an event with following definition should occur at 20100611 as the last instance, but it returns null time before returning 20100611 when I use icalrecur_iterator_next to iterate the recurrence, i.e., 20100610 is returned in the last iteration and then icaltime_is_null_time returns true.
DTSTART;VALUE=DATE:20100524
DTEND;VALUE=DATE:20100525
RRULE:FREQ=DAILY;UNTIL=20100611;WKST=SU