Use `pdfork` support where supported

[mathstuf]

Would it be possible to use procdesc to support #4? This would drop the need to register a signal handler.

FreeBSD manpages:

• pdwait4
• procdesc

[mathstuf]

Heh, pdwait4 is not implemented yet it seems. I suppose since we need poll anyways, wait4 could be used instead with the pid directly.

[alexcrichton]

Yeah unless there's a concrete technical reason that's compelling to do this, I'd probably avoid it.

[mathstuf]

Well, it'd be with the goal of getting #4 supportable on at least a few platforms. I don't know what to do about Linux; it seems that there are lots wanting a pdfork or forkfd syscall, but I haven't seen any progress anywhere on actually making it happen.

[alexcrichton]

Something like #4 is probably best done with tokio-process, not w/ just this crate in general

[mathstuf]

Ok, that sounds reasonable. Closing this.