[gimp] libgimpwidgets: avoid using a function only available since GTK+ 2.22

[Mikael Magnusson <mikachu src gnome org>]

commit 0e55c5e4d81b402f217b47f31855d77f5f8b6aa0
Author: Mikael Magnusson <mikachu src gnome org>
Date:   Sat Dec 18 00:31:22 2010 +0100

    libgimpwidgets: avoid using a function only available since GTK+ 2.22

 libgimpwidgets/gimpruler.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)
---
diff --git a/libgimpwidgets/gimpruler.c b/libgimpwidgets/gimpruler.c
index 271e46d..7e24279 100644
--- a/libgimpwidgets/gimpruler.c
+++ b/libgimpwidgets/gimpruler.c
@@ -1028,17 +1028,24 @@ gimp_ruler_make_pixmap (GimpRuler *ruler)
   GtkWidget        *widget = GTK_WIDGET (ruler);
   GimpRulerPrivate *priv   = GIMP_RULER_GET_PRIVATE (ruler);
   GtkAllocation     allocation;
+  cairo_t          *cr;
+  cairo_surface_t  *surface;
 
   gtk_widget_get_allocation (widget, &allocation);
 
   if (priv->backing_store)
     cairo_surface_destroy (priv->backing_store);
 
+  cr = gdk_cairo_create (gtk_widget_get_window (widget));
+  surface = cairo_get_target (cr);
+
   priv->backing_store = 
-    gdk_window_create_similar_surface (gtk_widget_get_window (widget),
-                                       CAIRO_CONTENT_COLOR,
-                                       allocation.width,
-                                       allocation.height);
+    cairo_surface_create_similar (surface,
+                                  CAIRO_CONTENT_COLOR,
+                                  allocation.width,
+                                  allocation.height);
+
+  cairo_destroy (cr);
 }