Unset current user after request is processed

[RyoheiTaima]

@daviddavis @Paessler @belugame @vokracko

Fix #14 Related #49

In addition to #49, I changed the test to check the current user in the session.

[alfonsrv]

@belugame can we get these changes in a new PyPI release?

[belugame]

I can't cause I m no longer part of the team. Your best bet is to contact the email in https://github.com/PaesslerAG/django-currentuser/blob/master/setup.py

[alfonsrv]

Thanks for the pointer. Email address doesn't accept mails from outside, but tried reaching out to Konstantin.