Add more attrs to the test accounts, for more testing
Add support for negative queries in set_search_seed
Replace ACLField with proper model functions and LDAPUserManager

Also, add silly tests

Examples:

    user1 = LDAPUser.objects.get(username='user1')
    print user1.is_infra()

    # return all objects that have 'developer.group' in ACL field
    developers = LDAPUser.objects.developers()

    # return all objects that do not have 'developer.group' in ACL
    non_developers = LDAPUser.objects.developers(False)
Add tests for the accounts lists