[libsigcplusplus] signal_emit: Make a_ private.

[Murray Cumming <murrayc src gnome org>]

commit 3059ee710b0c02beea4f8262b718c24af9b0a816
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 21 19:26:34 2016 +0200

    signal_emit: Make a_ private.

 sigc++/signal.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/sigc++/signal.h b/sigc++/signal.h
index 2958adf..c641f03 100644
--- a/sigc++/signal.h
+++ b/sigc++/signal.h
@@ -272,9 +272,9 @@ struct signal_emit
       slot_iterator_buf_type(slots.begin(), &self), slot_iterator_buf_type(slots.end(), &self));
   }
 
+private:
   std::tuple<type_trait_take_t<T_arg>...> a_;
 
-private:
   // TODO_variadic: Replace this with std::experimental::apply() if that becomes standard
   // C++, or add our own implementation, to avoid code duplication.
   template <std::size_t... Is>