Allow to override 'object' Lua property of CScriptBinderObject class

This allows to run Call of Chernobyl correctly (#1529).

Though, I'm not sure if it's right, but original luabind was allowing
writing to readonly objects anyway.

src/xrGame/script_binder_object_script.cpp

@@ -19,7 +19,7 @@ SCRIPT_EXPORT(CScriptBinderObject, (),
     module(luaState)
     [
         class_<CScriptBinderObject, no_bases, default_holder, CScriptBinderObjectWrapper>("object_binder")
-            .def_readonly("object", &CScriptBinderObject::m_object)
+            .def_readwrite("object", &CScriptBinderObject::m_object)
             .def(constructor<CScriptGameObject*>())
             .def("reinit", &CScriptBinderObject::reinit, &CScriptBinderObjectWrapper::reinit_static)
             .def("reload", &CScriptBinderObject::reload, &CScriptBinderObjectWrapper::reload_static)