Testing with Django 1.6 support

Tests pass, but I'm still confronted with a Django backtrace on `{% browserid_login %}`:

```
KeyError at /
'browserid_login'
Request Method:	GET
Request URL:	http://localhost:8080/
Django Version:	1.6
Exception Type:	KeyError
Exception Value:	
'browserid_login'
```

... might be unrelated with this extension though.