[libsigc++2/variadic_bind4] track_obj_functor: Do some perfect forwarding.

[Murray Cumming <murrayc src gnome org>]

commit 21e42edc850c996f5a0e8e5e250a06865862c304
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Mar 3 09:53:04 2016 +0100

    track_obj_functor: Do some perfect forwarding.

 sigc++/adaptors/track_obj.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/sigc++/adaptors/track_obj.h b/sigc++/adaptors/track_obj.h
index bc2a888..61830fc 100644
--- a/sigc++/adaptors/track_obj.h
+++ b/sigc++/adaptors/track_obj.h
@@ -74,10 +74,10 @@ public:
    */
   template <typename... T_arg>
   decltype(auto)
-  operator()(T_arg... _A_arg)
+  operator()(T_arg&&... _A_arg)
   {
     return this->functor_.SIGC_WORKAROUND_OPERATOR_PARENTHESES<type_trait_pass_t<T_arg>...>
-      (_A_arg...);
+      (std::forward<T_arg>(_A_arg)...);
   }
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS