Assign a bug to a user.

        param bugid: ``int``, bug ID number.
        param user: ``str``, the login name of the user to whom the bug is
                    assigned
        returns: deferred that when fired returns True if the change succeeded,
                 False if the change was unnecessary (because the user is
                 already assigned.)

def assign(self, bugids, user):
        """
        Assign a bug to a user.

        param bugid: ``int``, bug ID number.
        param user: ``str``, the login name of the user to whom the bug is
                    assigned
        returns: deferred that when fired returns True if the change succeeded,
                 False if the change was unnecessary (because the user is
                 already assigned.)
        """
        payload = {'ids': (bugids,), 'assigned_to': user}
        d = self.call('Bug.update', payload)
        d.addCallback(self._parse_bug_assigned_callback)
        return d