I want to let users specify options to be used with a PAM module,
using debconf. This means that I need to create the pam-config file
from postinst. Writing the result to /usr/share/pam-configs feels
wrong. It would be nice if pam-auth-update gave preference to files
in /var/lib/pam-configs. E.g. if /var/lib/pam-configs/passwdqc
existed, it would be used instead of
/usr/share/pam-configs/passwdqc.