Refactor get/set_property to take the item as first argument

lily/span-arpeggio-engraver.cc

Index: lily/span-arpeggio-engraver.cc
diff --git a/lily/span-arpeggio-engraver.cc b/lily/span-arpeggio-engraver.cc
index 7f15772200a72f8845bc832008565bceac12fc99..f9673ca3b3ab4bf2d8f921f4c5f66903167ab814 100644
--- a/lily/span-arpeggio-engraver.cc
+++ b/lily/span-arpeggio-engraver.cc
@@ -81,7 +81,7 @@ Span_arpeggio_engraver::process_acknowledged ()
 
   */
   if (!span_arpeggio_ && arpeggios_.size () > 1
-      && to_boolean (get_property ("connectArpeggios")))
+      && to_boolean (get_property (this, "connectArpeggios")))
     span_arpeggio_ = make_item ("Arpeggio", SCM_EOL);
 
   if (span_arpeggio_)
@@ -117,7 +117,7 @@ Span_arpeggio_engraver::stop_translation_timestep ()
             we can't kill the children, since we don't want to the
             previous note to bump into the span arpeggio; so we make
             it transparent.  */
-          arpeggios_[j]->set_property ("transparent", SCM_BOOL_T);
+          set_property (arpeggios_[j], "transparent", SCM_BOOL_T);
         }
 
       span_arpeggio_->set_parent (arpeggios_[0]->get_parent (Y_AXIS), Y_AXIS);