Prepares the ACL returned from the AWS API for comparison with a given one.

def _prep_acl_for_compare(ACL):
    '''
    Prepares the ACL returned from the AWS API for comparison with a given one.
    '''
    ret = copy.deepcopy(ACL)
    ret['Owner'] = _normalize_user(ret['Owner'])
    for item in ret.get('Grants', ()):
        item['Grantee'] = _normalize_user(item.get('Grantee'))
    return ret