Emitted when the cursor (not the selection) has moved.
You can move the cursor by pressing Ctrl and one of the arrow keys: There will be a dotted rectangle around the label of the current "cursor" item. By pressing space you can (un)select it.
The movement parameter will be 1 (Gtk::MOVEMENT_VISUAL_POSITIONS) when moving the cursor left or right, and 3 (Gtk::MOVEMENT_DISPLAY_LINES) when moving up or down.
FIXME: The second parameter seems to be -1 or 1 only, depending on the direction (backward or forward) you move.