[libsigc++2] deduce_result_t: Add initial T_return template parameter.

[Murray Cumming <murrayc src gnome org>]

commit 0a2f35906880e2a35183c844a8ce8910beb2960d
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Aug 14 23:12:31 2015 +0200

    deduce_result_t: Add initial T_return template parameter.
    
    To make it clearer that this is how to use it.

 sigc++/adaptors/macros/deduce_result_type.h.m4 |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/sigc++/adaptors/macros/deduce_result_type.h.m4 b/sigc++/adaptors/macros/deduce_result_type.h.m4
index 2f5d70c..c31da7d 100644
--- a/sigc++/adaptors/macros/deduce_result_type.h.m4
+++ b/sigc++/adaptors/macros/deduce_result_type.h.m4
@@ -93,8 +93,8 @@ struct deduce_result_type
 #ifndef DOXYGEN_SHOULD_SKIP_THIS
 FOR(0,CALL_SIZE,[[DEDUCE_RESULT_TYPE_ADAPTOR(%1,CALL_SIZE)]])dnl
 
-template<typename... T>
-using deduce_result_t = typename deduce_result_type<T...>::type;
+template<typename T_functor, typename... T_args>
+using deduce_result_t = typename deduce_result_type<T_functor, T_args...>::type;
 
 #endif // DOXYGEN_SHOULD_SKIP_THIS