[gtkmm] leave_notify in VBox

[Carl Nygard <cjnygard fast net>]

I'm trying to set up a callback to tell me when the mouse has left a
VBox widget area.  I've tried the signal_leave_notify_event, tried
overriding on_leave_notify_event, nothing seems to work.

I even made sure to add_mask(Gdk::LEAVE_NOTIFY_MASK), but nada...

What am I missing?

-- 
Carl Nygard <cjnygard fast net>