We'll force stdout+stderr to be a pipe the spawning client
controls, thus there's no need to lose error reporting by
prematurely redirecting stdout+stderr to /dev/null.
We can now rely exclusively on OnDestroy to write to syslog() on
uncaught die failures.
Also support falling back to oneshot mode on socket and cwd
failures, since some commands may still be useful if the current
working directory goes missing :P