[libsigcplusplus] limit_derived_target: Use perfect forwarding.

[Murray Cumming <murrayc src gnome org>]

commit eecc0b17fb4a46a8bf64aa79ffd3ec0055f056df
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Apr 1 10:01:38 2016 +0200

    limit_derived_target: Use perfect forwarding.

 sigc++/visit_each.h |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)
---
diff --git a/sigc++/visit_each.h b/sigc++/visit_each.h
index 5daaf85..7d4f27d 100644
--- a/sigc++/visit_each.h
+++ b/sigc++/visit_each.h
@@ -30,7 +30,8 @@ namespace internal
 
 template <class Base, class Derived>
 constexpr bool is_base_of_or_same_v =
-  std::is_base_of<Base, Derived>::value || std::is_same<Base, Derived>::value;
+  std::is_base_of<std::decay_t<Base>, std::decay_t<Derived>>::value ||
+    std::is_same<std::decay_t<Base>, std::decay_t<Derived>>::value;
 
 // This should really be an inner class of limit_derived_target, without the T_limit template type,
 // But the SUN CC 5.7 (not earlier versions) compiler finds it ambiguous when we specify a
@@ -63,10 +64,10 @@ struct limit_derived_target
   using T_self = limit_derived_target<T_target, T_action>;
 
   template <class T_type>
-  void operator()(const T_type& _A_type) const
+  void operator()(T_type&& _A_type) const
   {
     with_type<is_base_of_or_same_v<T_target, T_type>,
-      T_type, T_self>::execute_(_A_type, *this);
+      T_type, T_self>::execute_(std::forward<T_type>(_A_type), *this);
   }
 
   limit_derived_target(const T_action& _A_action) : action_(_A_action) {}
@@ -103,10 +104,10 @@ struct limit_derived_target<T_target*, T_action>
   using T_self = limit_derived_target<T_target*, T_action>;
 
   template <class T_type>
-  void operator()(const T_type& _A_type) const
+  void operator()(T_type&& _A_type) const
   {
     with_type_pointer<is_base_of_or_same_v<T_target, T_type>,
-      T_type, T_self>::execute_(_A_type, *this);
+      T_type, T_self>::execute_(std::forward<T_type>(_A_type), *this);
   }
 
   limit_derived_target(const T_action& _A_action) : action_(_A_action) {}