[libsigcplusplus] signal_base: Make notify() private.

[Murray Cumming <murrayc src gnome org>]

commit 6bd213d8abd0febfefe8eff0b2e7e8adcf193d04
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 21 12:26:42 2016 +0200

    signal_base: Make notify() private.

 sigc++/signal_base.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/sigc++/signal_base.h b/sigc++/signal_base.h
index 10d3623..4e334f5 100644
--- a/sigc++/signal_base.h
+++ b/sigc++/signal_base.h
@@ -166,6 +166,7 @@ struct SIGC_API signal_impl : public notifiable
   /// Removes invalid slots from the list of slots.
   void sweep();
 
+private:
   /** Callback that is executed when some slot becomes invalid.
    * This callback is registered in every slot when inserted into
    * the list of slots. It is executed when a slot becomes invalid