Add annotations for egg_list_box_select_child()
Add annotations for egg_list_box_select_child()

Mainly adding (allow-none) to the child parameter so that it is
allowed to pass null from language bindings.

https://bugzilla.gnome.org/show_bug.cgi?id=697593

GNOME/egg-list-box,GNOME/egg-list-box,GNOME/egg-list-box