When a spawned process terminates, goon may keep its input pipe open

[alco]

Investigate if that is the case. Originally reported in alco/porcelain#15.

[wawe]

I can reproduce this using the following steps:

1. Listen on a UNIX socket: $ echo 'Hello, world!' | socat UNIX-LISTEN:/tmp/test.sock -
2. In another terminal: $ goon -proto 1.0 -in=true -out=true socat UNIX-CONNECT:/tmp/test.sock -
   Expected: goon should print the message and terminate
   Actual: goon prints out "Hello, world!", but does not terminate. $ ps -A | grep socat shows socat <defunct>, so the child process has terminated. When I type some characters into stdin and press Enter, goon terminates with panic: write |1: broken pipe.

In my Elixir program, I currently work around this by exchanging inexpensive messages in 10-second intervals with the spawned process. Falling back to the basic driver also works.