Bring back the much more readable unified format for differences in
/etc/{group,master.passwd}. This was originally turned on for all of
/etc/{aliases,group,master.passwd} in r55196, but then backed out
only for the latter two in r56697, as the adaption of the sed(1)ing
done in r56308 was incorrect. This left us with inconsistent diff(1)
formats in the daily output of periodic(8) ever since, despite in
r56697 having been promised to be revisited. So properly adapt the
password hash filtering to the unified format and turn the later on
again for /etc/{group,master.passwd}, too.