Comment 1 for bug 438985

My fault! It's concerning that no tests broke. I incorrectly used 'is' to compare the user and person, when I should have used '=='.

Reading the view code also revealed another issue: there is a permission conflict. When setting the bug supervisor, you can set it to any person, or a team you administer. This implicitly adds a structural subscription for them. In other places you can only subscribe *yourself* or a team you administer. The latter restriction is now implemented in the model, so attempting to set the bug supervisor to another non-team person will fail similarly. I'm not sure how best to resolve this one.