(Linux) set dinit as child subreaper.
(Linux) set dinit as child subreaper.

This allows catching/watching double-forking processes even if we
are not PID 1. Double-fork orphans will be reparented to the
subreaper (i.e. Dinit) rather than PID 1 (init).

davmac314/dinit,davmac314/dinit,davmac314/dinit