Bug fix for the help of the chronology engine. 

Now the two first bubbles show the right answer.
Before this commit, they just blocked. Even if, they were counted as right, the displayed images weren't the good ones.
It was a problem with .animate(). It's explained here : http://www.screenfeed.fr/blog/jquery-1-5-remedier-au-bug-de-animate-avec-background-position-0296/.