[gthumb] add the app menu to the header-bar only if using gtk+ 3.12

[Paolo Bacchilega <paobac src gnome org>]

commit c8f653e4aaf0b7f1337ce3da6d85400ae8601f54
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sun Mar 29 19:58:38 2015 +0200

    add the app menu to the header-bar only if using gtk+ 3.12

 gthumb/gth-window.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gthumb/gth-window.c b/gthumb/gth-window.c
index ac059c9..a63f5f9 100644
--- a/gthumb/gth-window.c
+++ b/gthumb/gth-window.c
@@ -116,6 +116,7 @@ _gth_window_add_header_bar (GthWindow *self)
        gtk_widget_show (self->priv->headerbar);
        gtk_header_bar_set_show_close_button (GTK_HEADER_BAR (self->priv->headerbar), TRUE);
 
+#if GTK_CHECK_VERSION(3,12,0)
        {
                gboolean  shell_shows_app_menu;
                char     *decoration_layout;
@@ -139,6 +140,7 @@ _gth_window_add_header_bar (GthWindow *self)
 
                g_free (decoration_layout);
        }
+#endif
 
        self->priv->title = gth_window_title_new ();
        gtk_widget_show (self->priv->title);