Apply selected patches from OpenWall:
http://cvsweb.openwall.com/cgi/cvsweb.cgi/Owl/packages/vixie-cron/

1. Add PAM support.
2. Sanitize children process reaping
3. futimens when we have an fd
4. close_all for crontab(8)
5. use a table for spool dirs instead of duplicating code.
6. handle errors from process_exit()
7. Add ENABLE_FIX_DIRECTORIES ifdef and enable it by default for compat
8. Avoid using fd's < STDERR

Not applied:
1. no xfork (no setresuid)
2. did not do the lstat before open.
3. did not enable cron group