improved GetGraphCoordsFromPoint

[Wolfgang]

I'd like to suggest an enhanced version of the command GetGraphCoordsFromPoint.

Right now, the return status of this function indicates if the mouse cursor is within the plot area of the corresponding graph.

I'd like to have the possibility determining if the mouse cursor is above the plot area, i.e. within the plot area (pixelwise) and directly on top the plot area. 

The difference is in cases where the plot area is covered by other controls or menus: In this case (see the thread with example program here) the mouse may be well within the area, but not over the graph because the graph is covered (so the mouse cursor is over some other element)...

The motivation for this feature is the frequent wish to change the appearance of the mouse cursor: if it is located over the plot area, a cross hair cursor style might be more useful to indiciate e.g. mouse cursor coordinates, while if the mouse cursor is located above some other control element the cross hair cursor is disturbing and the default style is much more convenient.