fixed bug#6681: RST default reference role tries docutils' default role ...

Fixes bug#6681 as described in https://code.djangoproject.com/ticket/6681

Docutils establish a ''DEFAULT_INTERPRETED_ROLE'' which is overriden by django with **cmsreference** role.

Django's role is intended to work on admin docs, but it's not suitable for general purpose as it needs some keys in ''inliner.document.settings''.