Allow privileged users to assign issues to other users (filtered for sanity by role, subscription to issue, or other methods)

This is more useful for use of Project module off of Drupal.org: the ability to assign users other than oneself to issues.

Use case from our new project manager:

Also, would it be possible for you and me to sit down for a couple of hours so that I can learn how to use agaric's site to dole out tasks to you and Dan?

I'll be looking into doing this with a hook_form_alter for now, thoughts and input appreciated.

^{benjamin, Agaric Design Collective}