[glom] EggSpreadTableDndMM: Use newer sigc::signal syntax.

[Murray Cumming <murrayc src gnome org>]

commit 63e8e47710dccb0d64d03f43cee3a736e4c2417e
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Dec 16 16:42:37 2016 +0100

    EggSpreadTableDndMM: Use newer sigc::signal syntax.

 .../eggspreadtablemm/eggspreadtabledndmm.h         |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/glom/utility_widgets/eggspreadtablemm/eggspreadtabledndmm.h 
b/glom/utility_widgets/eggspreadtablemm/eggspreadtabledndmm.h
index a0a51eb..6ce031d 100644
--- a/glom/utility_widgets/eggspreadtablemm/eggspreadtabledndmm.h
+++ b/glom/utility_widgets/eggspreadtablemm/eggspreadtabledndmm.h
@@ -106,7 +106,7 @@ public:
    * <tt>void on_my_%widget_drop_possible()</tt>
    */
 
-  Glib::SignalProxy2< bool, Gtk::Widget*, bool& > signal_widget_drop_possible();
+  Glib::SignalProxy<bool(Gtk::Widget*, bool)> signal_widget_drop_possible();
 };
 
 } // namespace Egg