Modifying exception throwing in Sync::Digest

Now there are more diagnostic information attached to each exception
diff --git a/doc/doxygen_boost_dummy.h b/doc/doxygen_boost_dummy.h
index ffcc1b0..bfa0592 100644
--- a/doc/doxygen_boost_dummy.h
+++ b/doc/doxygen_boost_dummy.h
@@ -1,3 +1,6 @@
-namespace boost { template<class T> class shared_ptr { T *dummy; }; }
+namespace boost { 
+	template<class T> class shared_ptr { T *dummy; }; 
+	template<class T> class weak_ptr { T *dummy; }; 
+}
 
 namespace Sync { class DiffStateContainer { boost::shared_ptr<DiffState> dummy; }; }