Issue #24 fixed and discoverer/runner can now support non-standard test IDs

If our Django(<1.6) project contains any tests that don't have 'tests' substring in their ID's (e.g. doctests), then cricket fails with:

```
ValueError: list.index(x): x not in list
```

Steps to replicate:
* Add doctest to some function in empty Django project:

```
# urls.py

def test_func():
    '''
    Look on my doctests, ye Mighty, and despair:

    >>> test_func() == 42
    True
    '''
    return 42 
```

* Add suite generation code to __init__.py:

```
#coding: utf-8

import unittest
import doctest
import urls

def suite():
    suite = unittest.TestSuite()
    suite.addTest(doctest.DocTestSuite(urls))
    return suite
```

* Run test discoverer:

```
python ./manage.py test --testrunner=cricket.django.discoverer.TestDiscoverer djtest
```