Output was incorrect, partly to stdout and stderr, resp.
As Manolo noted in fltk.general, Fl_Window::screen_num() is the
correct API to retrieve the screen number of a window rather than
Fl::screen_num(...).
This is intended to be used as
(a) an example of event handling and
(b) a test program to visualize many event related variables
This first version is compatible with FLTK 1.3.x but lacks the screen
scaling factor under 1.3.x (which is always assumed to be 100%).
Note: this does not reflect any system or monitor related settings.