Handy because ls(1) helpfully converts the time to human-readable
format when printing, and because shell tools like "test -nt" and
"find -newer" can be used against it.
"Inspired" by a discussion about removing lockfiles older than the
last reboot, and Al Crooks' handy observation that a close
approximation can be found with /var/run/dmesg.boot
While here, notice that a lot of the kernfs structures and naming
changed suddenly, and though it seems a clear improvement, there was no
mention in commit logs.