* src/rbgtktreeview.c: Fix some methods of Gtk::TreeView to accept nil.
* src/rbgtktreeview.c: Fix some methods of Gtk::TreeView to accept nil.


kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2