Wait_VBL does not actually waits for a VBL about grafx2 HOT 5 CLOSED

Implemented a kind of retrace simulator in r166. It's limited by the accuracy 
of SDL
timers, which is limited by the OS : Probably 10ms under Windows.

No bad effects so far.

This one will have to wait for SDL 1.3 for a proper fix.
Anyways, the timing is not really critical, it's only used for two things, the 
spray 
and the sliders.
The function is also called when the program is idling now, so when converting 
it to 
a busy loop (polling the videocard or something like that), please take care.

Wait_VBL still called by :

-Input temporisation when idling, not time critical sync, waiting some random 
time 
is ok there.
-Freehand draw in "DESSIN_DISCONTINU". Probably a bad idea since we don't merge 
mouse events. This was right when polling the mouse directly on the ps/2 port 
under 
dos. Can probably be removed.

In any case, all these calls can probably be replaced by SDL_Delay(50000). So, 
marking this as invalid :)