security/unix-selfauth-helper: Update to 1.0.1

Add warning about base bug: pam_exec.so contained a bug that would
prevent the helper to work correctly in most cases. For 13.x-RELEASE,
add a script checking the patch level and displaying a warning on
installation.

Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D36115