Switched to boost::signals2

Index: src/editor/combobox.hpp
--- src/editor/combobox.hpp.orig
+++ src/editor/combobox.hpp
@@ -18,7 +18,7 @@
 #ifndef HEADER_PINGUS_EDITOR_COMBOBOX_HPP
 #define HEADER_PINGUS_EDITOR_COMBOBOX_HPP
 
-#include <boost/signal.hpp>
+#include <boost/signals2.hpp>
 
 #include "engine/display/sprite.hpp"
 #include "engine/gui/rect_component.hpp"
@@ -88,7 +88,7 @@ class Combobox : public GUI::RectComponent (public)
   
   void update_layout() {}
   
-  boost::signal<void (const ComboItem&)> on_select;
+  boost::signals2::signal<void (const ComboItem&)> on_select;
 
 private:
   Combobox();
