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

[Murray Cumming <murrayc src gnome org>]

commit 90e6f7216c644200e5dac0ba5624189ac4c3f294
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Mar 3 10:03:42 2016 +0100

    retype_return_functor: Do some perfect forwarding.

 sigc++/adaptors/retype_return.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/sigc++/adaptors/retype_return.h b/sigc++/adaptors/retype_return.h
index 56c0ac5..e01a00a 100644
--- a/sigc++/adaptors/retype_return.h
+++ b/sigc++/adaptors/retype_return.h
@@ -22,9 +22,9 @@ struct retype_return_functor : public adapts<T_functor>
 
 
   template <class... T_arg>
-  inline T_return operator()(T_arg... _A_a)
+  inline T_return operator()(T_arg&&... _A_a)
     { return T_return(this->functor_.SIGC_WORKAROUND_OPERATOR_PARENTHESES<T_arg...>
-        (_A_a...));
+        (std::forward<T_arg>(_A_a)...));
     }
 
   retype_return_functor() {}