Fixed #23758

- intentional breakage with recursion limit
- extents the alphabet ( to use multi letter ) for get alias prefix

executed from `test_subquery_condition` (queries.tests.Queries1Tests)
The tests fail on Python 3:

```python
Traceback (most recent call last):
  File ".../tests/queries/tests.py", line 391, in test_avoid_inifinite_loop_on_too_many_subqueries
    context.exception.message,
AttributeError: 'RuntimeError' object has no attribute 'message'
```

http://djangoci.com/job/django-pull-requests/1656/