[glade] Marking GtkOffscreenWindow since="2.20"

[Tristan Van Berkom <tvb src gnome org>]

commit 53f9cdf1e77d77128a4607d1e96b51161570fd79
Author: Tristan Van Berkom <tristan van berkom gmail com>
Date:   Sat Jan 29 19:38:34 2011 +0900

    Marking GtkOffscreenWindow since="2.20"

 plugins/gtk+/gtk+.xml.in |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/plugins/gtk+/gtk+.xml.in b/plugins/gtk+/gtk+.xml.in
index 9b26b10..fa64e7e 100644
--- a/plugins/gtk+/gtk+.xml.in
+++ b/plugins/gtk+/gtk+.xml.in
@@ -442,8 +442,8 @@ embedded in another object</_tooltip>
     </glade-widget-class>
 
     <glade-widget-class name="GtkOffscreenWindow" generic-name="offscreenwindow" _title="Offscreen Window" 
-			parent="GtkWindow" toplevel="True" default-width="440" default-height="250">
-
+			parent="GtkWindow" toplevel="True" default-width="440" default-height="250" 
+			since="2.20">
       <properties> 
 	<!-- Disable a handfull of properties that dont make sense for GtkOffScreenWindow
 	     (all window properties actually)