sendmail - pre-fork in daemon mode to avoid stall (2)

* disconnect() and set CurrentPid on pre-fork.  This fixes an issue where
  the boot console is revoked and enters getty before the backgrounded
  sendmail disconnects from the foreground process and tty, causing sendmail
  to complain in /var/log/maillog.

  This issue can occur due to myhostname() stalls when the internet is not
  available (e.g. /etc/resolv.conf is present but wifi-only system has not
  yet associated), or has other connectivity issues during boot.

Reported-by: Rolinh