[SDL] Mouse motion events incorrect after a new screen

[Stephen Anthony]

Sorry for replying to myself, but nobody else seems to be answering :(  
The reason this error is happening in 1.2.14 is because the SetMouseRange 
is new.  Previously, the mouse coordinates where calculated at the time of 
the mouse event, not clamped by SetMouseRange at the time of the 
ConfigureNotify event.

Of course, I'm not yet ruling out that something else in the app is 
causing an extra ConfigureNotify event.  I just can't seem to find it ...

SA