gdkScreenGetMonitorAtWindow
Returns the number of the monitor in which the largest area of the 
bounding rectangle of window resides.
gdkScreenGetMonitorAtWindow(object, window)
Since 2.2
[integer] the monitor number in which most of window is located,
or if window does not intersect any monitors, a monitor,
close to window.
Derived by RGtkGen from GTK+ documentation
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