title: How to remove all navigationbar back button title
body: <p>When I push a <code>UIViewController</code>, it has some title in back button at new <code>UIViewController</code>, if the title has a lot of text, It does not look good in iPhone 4s So I want to remove it.</p>
  
  <p>If I add some code in <code>prepareForSegue</code> function, it is going to be a trouble.</p>
  
  <p>Any better way to achieve this？</p>