Send a newsletter to all subscribers of more then one newsletter

We sent out different newsletters. Sometimes we like to send a special newsletter to all subscribers of all or several lists at once, but don't want to send a subscriber more then one special newsletter.
Simplenews doesn't allow you to send a newsletter to more then one newsletter together.
We patched the source to make this option available (patched attached).
To use this change the Multiple select setting in the newsletter taxonomy and select all newsletters in your newsletter node.
Per emailaddress the newsletter with the highest tid will be used to send it to.
Please add this feature to this version.