[glib] Improve some GNode docs

[Matthias Clasen <matthiasc src gnome org>]

commit cc44ef148c578ec87f71c155549a5d352a30bb3a
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Jul 8 19:26:25 2010 -0400

    Improve some GNode docs
    
    See bug 561248

 glib/gnode.h |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/glib/gnode.h b/glib/gnode.h
index f68e8b3..205d47c 100644
--- a/glib/gnode.h
+++ b/glib/gnode.h
@@ -250,7 +250,8 @@ GNode*	 g_node_last_sibling	 (GNode		  *node);
  *
  * Gets the previous sibling of a #GNode.
  *
- * Returns: the previous sibling of @node, or %NULL if @node is %NULL
+ * Returns: the previous sibling of @node, or %NULL if @node is the first
+ *     node or %NULL
  */
 #define	 g_node_prev_sibling(node)	((node) ? \
 					 ((GNode*) (node))->prev : NULL)
@@ -261,7 +262,8 @@ GNode*	 g_node_last_sibling	 (GNode		  *node);
  *
  * Gets the next sibling of a #GNode.
  *
- * Returns: the next sibling of @node, or %NULL if @node is %NULL
+ * Returns: the next sibling of @node, or %NULL if @node is the last node
+ *     or %NULL
  */
 #define	 g_node_next_sibling(node)	((node) ? \
 					 ((GNode*) (node))->next : NULL)