title: setFirstWeekday doesn't work
body: <p>I have an issue: <code>setFirstWeekDay</code> doesn't work... I don't know why ...</p>
  
  <pre><code> NSCalendar *gregorianT = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
      [gregorianT setFirstWeekday:2];
   NSDateFormatter *formatDayWeek = [[NSDateFormatter alloc] init];
      [formatDayWeek setDateFormat:@"c EEEE"];
  
      NSLog(@"date : %@  value for date : %@", dateForMonth, [formatDayWeek stringFromDate:dateForMonth]);
  </code></pre>
  
  <p>This is what I got:</p>
  
  <pre><code>date : 2012-11-23 14:18:28 +0000  value for date : 6 Friday
  </code></pre>
  
  <p>And I should get <code>date : 2012-11-23 14:18:28 +0000  value for date : 5 Friday</code></p>