timezone for 100.chksetuid

I would like to propose that a timezone setting be possible for the

	src/etc/periodic/security/100.chksetuid

script.  Either fix it at something like UTC, or add an rc.conf setting
that specifies what timezone to use.  Or both, default to UTC but allow
a timezone setting in rc.conf.

Reason for this is that for folk who travel, the 100.chksetuid script
generates and diffs "find -ls" output and this output changes if you
change timezones and update the system timezone setting while you are
away.  It then changes back again when you return.  If you travel a lot,
the two timezone changes cause this script to flag every setuid file as
having changed (twice), when all that changed is the time display.  This
means that real changes during the same period will likely be overlooked
and the frequent non-real diffs tend to make one likely to ignore this
section.

	-jr