title: jquery animate: two divs, one move out of screen, the other one move in
body: <p>I want to implement an animation, image there are two divs</p>
  
  <p>D1 | D2</p>
  
  <p>At first D2 is in screen(with 100% width), D1 is invisible(outside of screen).
  I want an animation that, D2 moves out to right, outside of screen.
  D1 moves from left to right, finally occupies the screen(replace D1).</p>
  
  <p>If you saw how Groupon animate when register user, you may understand what I mean...</p>
  
  <p>Thanks.</p>