title: flash[:notice] is shown on browser back again
body: <p>Hej, 
  i have a problem:
  I'm using flash[:notice] in my rails app. 
  A User comes to the page and creates a new object. The flash-message says "Created." Now he clicks on a link on the page. If he is coming back by using the "back" button of his browser the flash massage is presented again. 
  flash.now[:notice] doesnt work either (i think and i tested). The problem is that there is no new rendering of the file.</p>
  
  <p>Do you have any idea to prevent that? Thanks!</p>