oc-calendar: Extract time zone from TimeZoneDefinition

All-day and recurrent events have a binary property that describes the
time zone they take place in. We were using the user's time zone in
the webmail, but it may not be equal to the one in the client. This
difference eventually leads to time shifts in events.

OpenChange/MAPIStoreRecurrenceUtils.m

@@ -35,6 +35,7 @@
 #import <NGCards/iCalRepeatableEntityObject.h>
 #import <NGCards/iCalRecurrenceRule.h>
 #import <NGCards/iCalTimeZone.h>
+#import <NGCards/iCalTimeZonePeriod.h>
 
 #import "NSDate+MAPIStore.h"
 #import "MAPIStoreRecurrenceUtils.h"
@@ -51,7 +52,7 @@
                    fromRecurrencePattern: (struct RecurrencePattern *) rp
                           withExceptions: (struct ExceptionInfo *) exInfos
                        andExceptionCount: (uint16_t) exInfoCount
-                              inTimeZone: (NSTimeZone *) tz
+                              inTimeZone: (iCalTimeZone *) tz
 
 {
   NSCalendarDate *startDate, *olEndDate, *untilDate, *exDate;
@@ -63,7 +64,7 @@
   iCalWeekOccurrence weekOccurrence;
   iCalWeekOccurrences dayMaskDays;
   NSUInteger count, max;
-  NSInteger bySetPos;
+  NSInteger bySetPos, tzOffset;
   unsigned char maskValue;
 
   [entity removeAllRecurrenceRules];
@@ -242,9 +243,10 @@
           {
             /* The OriginalStartDate is in local time */
             exDate = [NSDate dateFromMinutesSince1601: exInfos[count].OriginalStartDate];
+            tzOffset = -[[tz periodForDate: exDate] secondsOffsetFromGMT];
             exDate = [exDate dateByAddingYears: 0 months: 0 days: 0
                                          hours: 0 minutes: 0
-                                       seconds: - [tz secondsFromGMT]];
+                                       seconds: tzOffset];
             [exceptionDates removeObject: exDate];
           }
       }