role key is assigned, but proper role name is not assigned

When the role is assigned, the value of the role in the $user object is supposed to be the role name, not the role ID. But roles assigned by autoassignrole are in the form

$user->roles[4] = 4

instead of the correct (assuming the 'kid' role is number 4):

$user->roles[4] = 'kid';

This often works, but is not correct.

The attached patch changes autoassignrole to use the role name as the value in the roles array.