implement overwrite mode

implement overwrite mode

2001-06-01  Havoc Pennington  <hp@redhat.com>

	* gtk/gtkentry.c (gtk_entry_commit_cb): implement overwrite mode

	* gtk/gtktextview.c (gtk_text_view_commit_handler): don't
	overwrite in overwrite mode if we already deleted the selection
	and replaced it with new text.

	* gtk/gtklabel.c (gtk_label_select_region_index): if you set the
	selection to an empty range, clear the clipboard if we owned it.
	(gtk_label_set_selectable): give up selection if we become
	unselectable.
	(gtk_label_state_changed): override state changed to unselect text
	when insensitive
	(get_text_callback): add paranoia check that indexes aren't
	outside of label->text
	(gtk_label_select_region): make -1 for start_offset mean "end of
	label," for consistency with GtkEditable

	* gtk/gtkmessagedialog.c (gtk_message_dialog_new): honor
	GTK_DIALOG_NO_SEPARATOR flag