updated gitdb to latest version

Sebastian Thiel · Sebastian Thiel · commit da5e58a47d3d · 2012-07-23T21:12:45.000+02:00
diff --git a/git/ext/gitdb b/git/ext/gitdb
@@ -1 +1 @@
-Subproject commit e96d2c381ef06667726eb745c67357de9d2a88fb
+Subproject commit ec6998f503e4619cd6bdecbbf372552ea126900a
