title: UIBarButtonItems invisible issue
body: <p>I have a toolbar added to the view in interface builder. And I need to add some buttons to it programmatically. So what I do is calling this method inside the viewDidLoad method. The items are added as the action method is executed but they are not visible.</p>
  
  <pre><code>- (void) addingNumberOfLettersBar {
  UIImage *image1 = [UIImage imageNamed:@"1"];
  UIButton *button1 = [UIButton buttonWithType:UIButtonTypeCustom];
  [button1 setImage:image1 forState:UIControlStateNormal];
  //UIBarButtonItem *barButtonItem1 = [[UIBarButtonItem alloc] initWithImage:image1 style:UIBarButtonItemStylePlain target:nil action:@selector(changeNumberOfLettersToShow:)];
  //UIBarButtonItem *barButtonItem1 = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:nil action:@selector(changeNumberOfLettersToShow:)];
  UIBarButtonItem *barButtonItem1 = [[UIBarButtonItem alloc] initWithCustomView:button1];
  barButtonItem1.tag = 1;
  
  UIImage *image3 = [UIImage imageNamed:@"3"];
  UIBarButtonItem *barButtonItem3 = [[UIBarButtonItem alloc] initWithImage:image3 style:UIBarButtonItemStylePlain target:nil action:@selector(changeNumberOfLettersToShow:)];
  barButtonItem3.tag = 3;
  
  UIImage *image4 = [UIImage imageNamed:@"4"];
  UIBarButtonItem *barButtonItem4 = [[UIBarButtonItem alloc] initWithImage:image4 style:UIBarButtonItemStylePlain target:nil action:@selector(changeNumberOfLettersToShow:)];
  barButtonItem4.tag = 4;
  
  UIImage *image5 = [UIImage imageNamed:@"5"];
  UIBarButtonItem *barButtonItem5 = [[UIBarButtonItem alloc] initWithImage:image5 style:UIBarButtonItemStylePlain target:nil action:@selector(changeNumberOfLettersToShow:)];
  barButtonItem5.tag = 5;
  
  UIImage *image5p = [UIImage imageNamed:@"5+"];
  UIBarButtonItem *barButtonItem5p = [[UIBarButtonItem alloc] initWithImage:image5p style:UIBarButtonItemStylePlain target:nil action:@selector(changeNumberOfLettersToShow:)];
  barButtonItem5p.tag = 0;
  
  UIBarButtonItem *flexibleItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];
  
  NSArray *toolbarItems = [NSArray arrayWithObjects:barButtonItem1, flexibleItem, barButtonItem3, flexibleItem, barButtonItem4, flexibleItem, barButtonItem5, flexibleItem, barButtonItem5p, nil];
  
  
  self.toolbar.items = toolbarItems;  
  }
  </code></pre>