[gnome-boxes] Update libgd module

[Alexander Larsson <alexl src gnome org>]

commit 3d7b7fd75a8b1f439b295c115910c537c721cfe3
Author: Alexander Larsson <alexl redhat com>
Date:   Wed Sep 26 11:33:31 2012 +0200

    Update libgd module
    
    We need this for gd_main_toolbar_add_widget()
    
    https://bugzilla.gnome.org/show_bug.cgi?id=684858

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 16cc32d..516d258 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 16cc32dd2d6837d24efcf16d3af94a9ac53172ff
+Subproject commit 516d2582a87bc72672d3c1d3a5a4d37a8aa7df3f