[gtk+] docs: add GTK_TREE_SORTABLE_*_COLUMN_ID to docs

[William Jon McCann <mccann src gnome org>]

commit 650d25cdafbb3f07dcd922542fda9f5af8c81b83
Author: William Jon McCann <william jon mccann gmail com>
Date:   Tue Jan 21 15:40:50 2014 -0500

    docs: add GTK_TREE_SORTABLE_*_COLUMN_ID to docs

 docs/reference/gtk/gtk3-sections.txt |    2 ++
 gtk/gtktreesortable.h                |   18 ++++++++++++++++++
 2 files changed, 20 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gtk/gtk3-sections.txt b/docs/reference/gtk/gtk3-sections.txt
index 66885a2..707dea5 100644
--- a/docs/reference/gtk/gtk3-sections.txt
+++ b/docs/reference/gtk/gtk3-sections.txt
@@ -4430,6 +4430,8 @@ gtk_tree_selection_get_type
 GtkTreeSortable
 GtkTreeSortableIface
 GtkTreeIterCompareFunc
+GTK_TREE_SORTABLE_DEFAULT_SORT_COLUMN_ID
+GTK_TREE_SORTABLE_UNSORTED_SORT_COLUMN_ID
 gtk_tree_sortable_sort_column_changed
 gtk_tree_sortable_get_sort_column_id
 gtk_tree_sortable_set_sort_column_id
diff --git a/gtk/gtktreesortable.h b/gtk/gtktreesortable.h
index ae3cabe..c9508b5 100644
--- a/gtk/gtktreesortable.h
+++ b/gtk/gtktreesortable.h
@@ -35,6 +35,24 @@ G_BEGIN_DECLS
 #define GTK_IS_TREE_SORTABLE(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GTK_TYPE_TREE_SORTABLE))
 #define GTK_TREE_SORTABLE_GET_IFACE(obj)  (G_TYPE_INSTANCE_GET_INTERFACE ((obj), GTK_TYPE_TREE_SORTABLE, 
GtkTreeSortableIface))
 
+/**
+ * GTK_TREE_SORTABLE_DEFAULT_SORT_COLUMN_ID:
+ *
+ * The GTK_TREE_SORTABLE_DEFAULT_SORT_COLUMN_ID can be used to make a
+ * #GtkTreeSortable use the default sort function.
+ *
+ * See also gtk_tree_sortable_set_sort_column_id()
+ */
+
+/**
+ * GTK_TREE_SORTABLE_UNSORTED_SORT_COLUMN_ID:
+ *
+ * The GTK_TREE_SORTABLE_DEFAULT_SORT_COLUMN_ID can be used to make a
+ * #GtkTreeSortable use no sorting.
+ *
+ * See also gtk_tree_sortable_set_sort_column_id()
+ */
+
 enum {
   GTK_TREE_SORTABLE_DEFAULT_SORT_COLUMN_ID = -1,
   GTK_TREE_SORTABLE_UNSORTED_SORT_COLUMN_ID = -2