Add hook_fork so plugins can fork their own workers.

[smfreegard]

This is to fix an annoyance I have on my spam trap. I start up a bunch of HTTP proxies in hook_init_master which starts the listeners etc.

The problem with this is that if one of them crashes, then it completely brings down Haraka as the master process dies. It's also sub-optimal from a performance standpoint as the master is then dealing with some really busy sockets.

I can't put the HTTP listeners in hook_init_child because the sockets are so busy it affects SMTP handling as the event-loop becomes saturated.

So I'd like to look into a way of creating a hook_fork which when run under cluster would fork nodes= children, assign their process.title to the plugin name and then manage respawning them.

[msimerson]

moved to ideas section of wiki