Merging from https://tabo@bitbucket.org/lukaszb/django-treebeard
Merging from https://tabo@bitbucket.org/lukaszb/django-treebeard

This allows the documentation to be generated without treebeard installed.

Thanks lukaszb for your contribution.

Ernsting/django-treebeard,Ernsting/django-treebeard,Ernsting/django-treebeard