The getModuleItemList function should not cache absolute_url_path as it
may vary according to where the script is called from. Here we generate
the cache key to also vary according to the same condition as the module
absolute_url_path results.

_portal_url_  _________called_from_url_________ -> __portal_url_VirtualRootPhysicalPath___  ________module.absolute_url_path_______  _result_
/erp5         /erp5/...                            /erp5                                    /erp5/my_module                          OK
/erp5         /erp5/web_site_module/my_site/...    /erp5                                    /erp5/web_site_module/my_site/my_module  BAD
/erp5/        /erp5/web_site_module/my_site/...    /erp5/web_site_module/my_site            /erp5/web_site_module/my_site/my_module  OK