Call daemon with 0 as first argument so that it changes the cwd to /.

Call daemon with 0 as first argument so that it changes the cwd to /.
It is not a problem in slowcgi since it calls chroot(2) and then
chdir(2) shortly afterwards but hopefully prevents copying code into
daemons where it does matter.
Problem first observed by dlg in ntpd(8) which keeps sitting in the
directory from where it was started which might for example prevent an
unmount.
Discussed with deraadt@