Significant string changes:
* sitepolicies, core_admin - 'Site policies' changed to 'Site security
settings'
* processexpirationstask, enrol_paypal - more explanatory name
* sitepolicy_help and sitepolicyguest_help, core_admin - setting will
only have an effect if the site policy handler is set to default
* sitepolicyhandler_desc,core_admin - improved wording
* pathtodot_help, core_admin - Windows and Mac paths
* debugstringids_desc, core_admin - improved explanation