oc: return last modified messages when sorted by PidMessageTagDeliveryTime

This change is required as oxcfxics is asking for sorting
using this property.

We fake this property on GCS folders (Tasks, Calendar, Contacts)
using c_lastmodified column.

OpenChange/MAPIStoreTasksMessageTable.m

@@ -157,6 +157,9 @@ static Class MAPIStoreTasksMessageK = Nil;
                           forKey: MAPIPropertyKey (PidLidTaskDueDate)];
       [knownProperties setObject: @"c_creationdate"
                           forKey: MAPIPropertyKey (PidLidTaskOrdinal)];
+      /* Use by oxcfxics to sort the latest first */
+      [knownProperties setObject: @"c_lastmodified"
+                          forKey: MAPIPropertyKey (PidTagMessageDeliveryTime)];
     }
 
   return [knownProperties objectForKey: MAPIPropertyKey (property)];