Drop references held by any GUI Lua script after execution

gtk2_ardour/luainstance.cc

@@ -1432,7 +1432,7 @@ LuaInstance::session_going_away ()
 
 	lua_State* L = lua.getState();
 	LuaBindings::set_session (L, _session);
-	lua.do_command ("collectgarbage();");
+	lua.collect_garbage ();
 }
 
 void

gtk2_ardour/luawindow.cc

@@ -329,6 +329,7 @@ LuaWindow::run_script ()
 			append_text (string_compose (_("C++ Exception: %1"), "..."));
 		}
 	}
+	lua->collect_garbage ();
 }
 
 void