Combinator is a tool for managing branch-based development in subversion repositories like Twisted's.
If you have bzr, you can obtain Combinator by running the following commands from your project directory:
mkdir Divmod bzr branch lp:divmod.org Divmod/trunk
If you neither have nor want bzr, you can download the divmod.org files as a tgz archive. Extract it and rename the "divmod.org" directory to "Divmod."
Then read Divmod/trunk/Combinator/README.txt and follow the directions there.
The directory names are significant. If Combinator is not within a Divmod/trunk directory, you're likely to see an error like "Combinator sitecustomize located outside of Combinator directory, aborting."