Adjust postmaster to recognize that a lockfile containing its parent's PID

Adjust postmaster to recognize that a lockfile containing its parent's PID
must be stale.  Tweak example startup scripts to not use pg_ctl but launch
the postmaster directly, thereby ensuring that only the postmaster's direct
parent shell will be a postgres-owned process.  In combination these should
fix the longstanding problem of the postmaster sometimes refusing to start
during reboot because it thinks the old lockfile is not stale.