[gtk+] Fix build by adding include

[Alexander Larsson <alexl src gnome org>]

commit 06a20d207a7868f37ab037a0a0c18aa14ad13c92
Author: Alexander Larsson <alexl redhat com>
Date:   Thu Nov 10 17:39:33 2011 +0100

    Fix build by adding include
    
    build failed with a GTK_IS_VIEWPORT link error

 gtk/gtkscrolledwindow.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 3bd5f3b..12fa27d 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -34,6 +34,7 @@
 #include "gtkscrollbar.h"
 #include "gtkscrolledwindow.h"
 #include "gtkwindow.h"
+#include "gtkviewport.h"
 #include "gtkprivate.h"
 #include "gtktypebuiltins.h"
 #include "gtkintl.h"