MergeProcess,spawn: unregister SIGCHLD and wakeup_fd (bug 655656)

In order to prevent forked processes from invoking the parent process's
SIGCHLD handler and writing to wakeup_fd (triggering BlockingIOError),
unregister the SIGCHLD and wakeup_fd.

Bug: https://bugs.gentoo.org/655656
Reported-by: Helmut Jarausch <jarausch@igpm.rwth-aachen.de>
2 files changed