2.1.5

The 2.1.5 release is actually a tiny bug fix release that I'm combining with
the large 2.1.4 release.

• Bugfix for socket.SO_REUSEPORT.

• Squashed bugs related to socket.socket failing in child processes.
  These squashed bugs fix IPv6 which had a tendency of not working as expected.

• Added communication between supervisor and children, allow children to be
  restarted if they fail to communicate to the supervisor.

• Added mode= and delay= optionals to the listen and
  :ref:tls_listen directives. Allowing listeners to spawn on specific ports
  and act in different ways.

  When mode and delay are configured in a listener directive, that
  listener will ignore the global mode and delay options for that listener.
  Setting mode and delay on a listener will also disable
  dynamic-switches for that listener, automatically.

• Internal module loading changes

• Added test utilities to the test suite.

• The blackhole environment will be reset for each test.

• Added a lot of testing to supervisor, worker and child functionality.

• Added a --quiet mode to suppress warnings when using
  -ls/--less-secure, running as the root user or not using the
  :ref:tls_dhparams option.

• Added a warning when running the server as the root user without specifying
  a reduced privilege user and group.

• Improved shutdown procedure, now does a much better job of disconnecting
  clients and closing everything before exiting.

• Added an internal counter of invalid SMTP commands. Mitigate DoS attacks,
  maximum failed commands per connection is 10. Clients that violate this rule
  get disconnected.