[gtk+] Add 'Since 2.20' documentation.

[Cody Russell <bratsche src gnome org>]

commit 4681f0b4677baef7b55d6b729883c4ea74a9a12c
Author: Cody Russell <crussell canonical com>
Date:   Mon Dec 28 09:23:05 2009 -0600

    Add 'Since 2.20' documentation.

 gtk/gtkoffscreenwindow.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkoffscreenwindow.c b/gtk/gtkoffscreenwindow.c
index fb6b9d9..2b9b415 100644
--- a/gtk/gtkoffscreenwindow.c
+++ b/gtk/gtkoffscreenwindow.c
@@ -247,6 +247,8 @@ gtk_offscreen_window_init (GtkOffscreenWindow *window)
  * hierarchy, gtk_widget_get_snapshot() can be used instead.
  *
  * Return value: A pointer to a #GtkWidget
+ *
+ * Since: 2.20
  **/
 GtkWidget *
 gtk_offscreen_window_new (void)
@@ -262,6 +264,8 @@ gtk_offscreen_window_new (void)
  * resizes then you should add a reference to it.
  *
  * Returns: A #GdkPixmap pointer to the offscreen pixmap, or %NULL.
+ *
+ * Since: 2.20
  **/
 GdkPixmap *
 gtk_offscreen_window_get_pixmap (GtkOffscreenWindow *offscreen)
@@ -280,6 +284,8 @@ gtk_offscreen_window_get_pixmap (GtkOffscreenWindow *offscreen)
  * needed.
  *
  * Returns: A #GdkPixbuf pointer, or %NULL.
+ *
+ * Since: 2.20
  **/
 GdkPixbuf *
 gtk_offscreen_window_get_pixbuf (GtkOffscreenWindow *offscreen)