Test failure fix

[Denis Darii]

Minor fix to prevent test(test_update_user_details_long_names) failure on release 0.4 and current trunk.

If you try:
$ ./manage.py test django_openid_auth.OpenIDBackendTests.test_update_user_details_long_names

the output:

Creating test database for alias 'default'...
E
======================================================================
ERROR: test_update_user_details_long_names (django_openid_auth.tests.test_auth.OpenIDBackendTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/dnx/workspace/envs/doauth/lib/python2.6/site-packages/django_openid_auth/tests/test_auth.py", line 132, in test_update_user_details_long_names
    self.backend.update_user_details(user, data, response)
  File "/home/dnx/workspace/envs/doauth/lib/python2.6/site-packages/django_openid_auth/auth.py", line 271, in update_user_details
    user.username = self._get_available_username(details['nickname'], openid_response.identity_url)
KeyError: 'nickname'

----------------------------------------------------------------------
Ran 1 test in 0.002s

FAILED (errors=1)

[Chris Johnston (cjohnston)]

This patch does not work for me with django 1.4