It looks like bootstrap.py was removed in late July, marked as obsolete. I followed these instructions to get mailman and postorious running, except I replaced the bootstrap.py step with the following:

virtualenv --system-site-packages /path/to/your/installation
$ source /path/to/your/installation/bin/activate
$ python setup.py install

Now, if you get weird errors, remove the --system-site-packages from your virtualenv and try again. I guess depending on how your system is setup, it may or may not work with that option.