Regarding my question above, with Richard Wackerbarth's help, I have
resolved my issue. The issue is that if one is running in an active
virtualenv, with sphinx installed globally but not in the virtualenv,
you have to either install sphinx in the virtualenv or run setup with
the global python, e.g. '/usr/bin/python setup.py build_sphinx'.
In addition to the requirement for sphinx, the src/mailman/docs/8-miles-
high.rst document uses the sphinx graphviz extension and requires that
at least the 'dot' command (part of graphviz) be installed somewhere in
the current path.
** Summary changed:
- Documentation fails to specifying sphinx requirement
+ Documentation fails to specify sphinx requirement and graphviz requirement.