Fix #iss1509

[AlvaroLQueiroz]

No description provided.

[acdha]

It looks like this will be moot with #1504 which updates build_solr_schema. The tests are failing for the other changes because through at least Django 1.11 Template.render() still requires a Context instance. It looks like the point of confusion was the API change which added pluggable backends which introduced the possibility of get_template or select_template returning something which is not django.template.Template:

https://docs.djangoproject.com/en/1.10/ref/templates/upgrading/#get-template-upgrade-django-18