Log Message:
py-supervisor: updated to 4.2.0

4.2.0:

- When ``supervisord`` is run in the foreground, a new ``--silent`` option
  suppresses the main log from being echoed to ``stdout`` as it normally
  would.

- Parsing ``command=`` now supports a new expansion, ``%(numprocs)d``, that
  expands to the value of ``numprocs=`` in the same section.

- Web UI buttons no longer use background images.

- The Web UI now has a link to view ``tail -f stderr`` for a process in
  addition to the existing ``tail -f stdout`` link.  Based on a
  patch by OuroborosCoding.

- The HTTP server will now send an ``X-Accel-Buffering: no`` header in
  logtail responses to fix Nginx proxy buffering.

- When ``supervisord`` reaps an unknown PID, it will now log a description
  of the ``waitpid`` status.

- Fixed a bug introduced in 4.0.3 where ``supervisorctl tail -f foo | grep bar``
  would fail with the error ``NoneType object has no attribute 'lower'``.  This
  only occurred on Python 2.7 and only when piped.