Check IP address not only login action but and during work session

I have prepared a patch to userone that performs a check of the remote ip address against authorised ip addresses every time a form is built. If the remote address is not in the authorised list, then the form is replaced with a warning, effectively preventing all administration activity.

The list of authorised ip addresses is saved into the $_SESSION array at login so that changes to it during the session do not immediately kill the ability of that administrator to work. This will allow a change of authorised addresses to happen in an orderly manner, or to enable a mistake in entering addresses to be corrected before the end of the session.

Patch attached. Please review and include if acceptable.

Regards.

Found an error in the original patch that caused problems when no addresses were specified. Patch re-rolled to fix that

Closing because Drupal 6 is no longer supported. If the issue verifiably applies to later versions, please reopen with details and update the version.