"Send to Both" option causes errors on user registration and failing email

Attached is a patch that:
1. addresses that issue of "Send to both" giving error message to register user.
2. Removes duplicate email addresses from send to list, if any
3. Removes empty log message that carries no meaning

Oh, I see, you're right - it won't catch duplicates if there are multiple addresses in the "Send notifications to this custom email address:" field. I know how to fix that though. New patch attached. The trick is using preg_split():

$emails = preg_split('/,[\w]+/', variable_get('user_register_notify_mailto', $from));