Replacing a notification with the same ID may result into canceling both (Fix for #135)

## ChangeLog

#### Version 0.7.4 (not yet released)

- [bugfix:] Platform specific properties were ignored.

- [bugfix:] cancel may throw an error if the OS returns NIL values (iOS).

- [bugfix:] Replacing a notification with the same ID may result into canceling both (iOS).

#### Version 0.7.3 (16.03.2014)

- [bugfix:] cancel callbacks have not been fired after all notifications have been canceled on iOS.

- [change:] The `oncancel` callback will be called at last if `autoCancel` is set to true (iOS).

        if ([self isNotificationScheduledWithId:id]) {

            UILocalNotification* notification = [self notificationWithId:id];

            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0.3 * NSEC_PER_SEC),

                           dispatch_get_main_queue(), ^{

                [self cancelNotification:notification fireEvent:NO];

            });

        }

        [self scheduleNotificationWithProperties:properties];