Custom Gtk3 Widget - scroll_event

[Bernhard Schuster <schuster bernhard gmail com>]

hey!

I am trying to derive a custom widget from GtkWidget. (Yet another 
approach to plot data, I got some special fancy requirements).
So I thought I could just overwrite the scroll_event 
handler/function-pointer and get hold of all scroll events on that 
widget. But it does not work as expected, the functions gets _never_ 
called at all.

I also tried to use `gtk_widget_{set_sensitive,set_focus,add_events}` 
but none fixed the issue nor did connecting to the "scroll-event" 
signal yield any callback executions.

For full demmo source code (yes, a minimal compileable example) is 
included in the following Stackoverflow question:
http://stackoverflow.com/questions/22738105/event-callback-does-not-get-executed-in-custom-gtk3-widget

Thanks a lot advance!

Best

Bernhard