Update import of basic recurrence rules

Conversion of COUNT to UNTIL was a simple calculation which assumed one
repetiton per period (day, week, month or year); it does not take exception
days and invalid dates into account. Solved by a new function which returns the
n'th occurrence of a recurrence rule.

In calcurse UNTIL is interpreted as a day (DATE), in RFC 5545 as a time of day
(DATE-TIME). This has implications when a recurrence rule has an occurrence on
the UNTIL day, see comment in ical.c

An "Import:" note is added when a multi-day event is imported and turned into a
calcurse all-day event.

Icalendar quotes in comments have been updated to RFC 5545.

Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

test/ical-009.sh

@@ -17,10 +17,10 @@ if [ "$1" = 'actual' ]; then
   rm -rf .calcurse || exit 1
 elif [ "$1" = 'expected' ]; then
   cat <<EOD
-Import process report: 0116 lines read
-2 apps / 0 events / 1 todo / 18 skipped
+Import process report: 0127 lines read
+2 apps / 0 events / 1 todo / 20 skipped
 VEVENT [12]: invalid or malformed event start time.
-VEVENT [17]: recurrence frequency not recognized.
+VEVENT [17]: rrule frequency not supported.
 VEVENT [23]: malformed summary line.
 VTODO [28]: item priority is invalid (must be between 0 and 9).
 VEVENT [32]: malformed exceptions line.
@@ -36,7 +36,9 @@ VEVENT [89]: invalid end time value type.
 VEVENT [94]: invalid until format.
 VEVENT [100]: invalid exception date value type.
 VEVENT [107]: invalid exception.
-VTODO [114]: The ical file seems to be malformed. The end of item was not found.
+VEVENT [114]: either end or duration.
+VEVENT [120]: end must be later than start.
+VTODO [125]: The ical file seems to be malformed. The end of item was not found.
 101
 EOD
 else