Support the situation when VC is pushed by UINavigationController, not adding Done button

[innocarpe]

1. I found a bug(maybe) when I use viewController(:sender:) to push CarteViewController.
   It couldn't find a back button when in the left side of UINavigationBar.
   It removes the back button made by UINavigationBar so that I can't back to previous screen.
   When I tap the done button, whole UINavigationViewController stack is dismissed.

I tried self.navigationItem.backBarButtonItem it also returned nil.

I suggest this PR to avoid this situation. I can't use now this because of this situation.

If this Done button would be an option, it has more chance to be used by other programmers.

2. I added super.viewWillAppear(). As I know, this is basically recommended.
   http://stackoverflow.com/questions/3348204/what-does-super-viewwillappear-do-and-when-is-it-required

[devxoul]

1. Thank you for pointing it out :) How about setting leftBarButtonItem along if the view controllers is pushed or presented? This approach is what I'm using in my company project. I think it's better than creating an extra property.

   // pushed
   if self.navigationController?.viewControllers.count > 1 {
       self.navigationItem.leftBarButtonItem = nil
   }
   // presented
   else if self.presentingViewController != nil && self.navigationItem.leftBarButtonItem == nil {
       self.navigationItem.leftBarButtonItem = UIBarButtonItem(
           barButtonSystemItem: .Done,
           target: self,
           action: "doneButtonDidTap"
       )
   }

2. Thank you. How about splitting commits? 1) and 2) are obviously different.

Thanks for your work :)

[innocarpe]

@devxoul Thank you for your feedback. With your code programmers doesn't need to consider both situations. I like the 'It just works' ways. I couldn't split the commit 1) and 2) because it is already uploaded to github.

I reset the commits to develop and made a commits, and merged to the one in github. Is there better way to accomplish this?

[devxoul]

@kwosu87, thanks. It'll be better rebase commits.