[gnome-boxes/gnome-3-6] Update to latest libgd

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit 6ab20cf848aa1a2d1c081e39a672b118db608f20
Author: Zeeshan Ali (Khattak) <zeeshanak gnome org>
Date:   Thu Nov 8 11:08:14 2012 +0100

    Update to latest libgd
    
    This is to get the fix for bug#687286.

 libgd |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgd b/libgd
index 516d258..6318d52 160000
--- a/libgd
+++ b/libgd
@@ -1 +1 @@
-Subproject commit 516d2582a87bc72672d3c1d3a5a4d37a8aa7df3f
+Subproject commit 6318d529754dbb2a5f95d3a546340f476b37bcc4