[libsigcplusplus] signal_emit: Make constructor explicit.

[Murray Cumming <murrayc src gnome org>]

commit 78f9b5c90b0830a401bc298deb8127610c329e9c
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 21 23:43:48 2016 +0200

    signal_emit: Make constructor explicit.

 sigc++/signal.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/sigc++/signal.h b/sigc++/signal.h
index 11ec37b..0a09d28 100644
--- a/sigc++/signal.h
+++ b/sigc++/signal.h
@@ -238,7 +238,7 @@ struct signal_emit
    * The parameters are stored in member variables. operator()() passes
    * the values on to some slot.
    */
-  signal_emit(type_trait_take_t<T_arg>... a) : a_(a...) {}
+  explicit signal_emit(type_trait_take_t<T_arg>... a) : a_(a...) {}
 
   /** Invokes a slot using the buffered parameter values.
    * @param slot Some slot to invoke.