implement a -n, --nofork option to run in the foreground (cda6dcd from 0.9)

git-svn-id: http://arthurdejong.org/svn/nss-pam-ldapd/nss-pam-ldapd-0.8@2020 ef36b2f9-881f-0410-afb5-c4e39611909c