Apply patch from Enrico Zini to improve ball movement

Apply patch from Enrico Zini to improve ball movement

From the mail:
if I understood correctly, the position of the ball is
updated, then the keyboard events are read, then the
screen is redisplayed. It should be instead: the screen
is redisplayed, then keyboard events are read and handled,
then the ball position is updated: that way the keyboard
event is connected with what is on the screen, which is
what the player would expect.