Add experimental support for crypted password

[linnea-s]

Hi, I've written a quick patch which implements support for crypted passwords. This makes it possible to put a password hash in /etc/sysrqd.secret with a command like "mkpasswd -m sha-512 > /etc/sysrqd.secret". The code attempts to detect a crypted password, so that cleartext passwords still work.

The motivation for this patch comes from diskless workstations and thin clients, which basically have world-readable NFS root filesystems so that the sysrqd password could be read by anybody. For this case something like bcrypt would be better, but I chose to use glibc's crypt for simplicity and to avoid additional dependencies.

[jd]

This looks like a good idea. Let me know if you want me to tag a release with that patch then.

[linnea-s]

That would be great. :)

[jd]

I tagged v15.