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-005.sh

@@ -7,6 +7,7 @@ if [ "$1" = 'actual' ]; then
   cp "$DATA_DIR/conf" .calcurse || exit 1
   "$CALCURSE" -D "$PWD/.calcurse" -i "$DATA_DIR/ical-005.ical"
   "$CALCURSE" -D "$PWD/.calcurse" -s10/03/2013 -r3
+  cat "$PWD/.calcurse/notes"/*
   rm -rf .calcurse || exit 1
 elif [ "$1" = 'expected' ]; then
   cat <<EOD
@@ -20,6 +21,7 @@ Import process report: 0023 lines read
 
 10/04/13:
  * Two days
+Import: multi-day event changed to one-day event
 EOD
 else
   ./run-test "$0"