oc-mail: Give support to store extra properties in versions message

This is handy when you want to store properties once a mail
has hit the server and thus cannot be changed.

OpenChange/MAPIStoreMailFolder.h

@@ -55,6 +55,11 @@
 - (NSData *) changeKeyForMessageWithKey: (NSString *) messageKey;
 - (NSData *) predecessorChangeListForMessageWithKey: (NSString *) messageKey;
 
+/* Extra properties from mail messages that already hit the server */
+- (void) setExtraProperties: (NSDictionary *) props
+                 forMessage: (NSString *) messageKey;
+- (NSDictionary *) extraPropertiesForMessage: (NSString *) messageKey;
+
 @end
 
 /* MAPIStoreOutboxFolder is a special subclass of MAPIStoreMailFolder where