title: Redmine allow user to view only one issue
body: <p>I have a Redmine installation and would like the ability to grant a user the ability to view (and maybe update) a single issue (not all issues in the project). The catch is that the issue is reported by someone else.</p>
  
  <p>Use Case:
  Users A,B, and admin C</p>
  
  <ol>
  <li>admin C creates two bug reports 1 and 2</li>
  <li>admin C wants to grant view access to user A on bug 1</li>
  <li>admin C wants to grant view access to user B on bug 2</li>
  <li>User A should not be able to access bug2</li>
  <li>User B should not be able to access bug1</li>
  </ol>
  
  <p>Can this be done with Redmine?  I have been messing around with the settings, but I don't see an easy way to accomplish this use case.</p>
  
  <p>If not, are there other bug trackers that do allow for such a use case?</p>