rename to _gtk_tree_selection_row_is_selectable and export internally,

rename to _gtk_tree_selection_row_is_selectable and export internally,

2006-03-01  Kristian Rietveld  <kris@imendio.com>

	* gtk/gtktreeselection.c (row_is_selectable): rename to
	_gtk_tree_selection_row_is_selectable and export internally,
	(gtk_tree_selection_real_select_node): changed so it is always
	possible to unselect insensitive nodes, changed the logic a bit to
	be more clear.

	* gtk/gtktreeprivate.h: add _gtk_tree_selection_row_is_selectable.

	* gtk/gtktreeview.c (gtk_tree_view_row_changed): Unselect a row if
	it became insensitive.