crontab entry environment variables [PSARC/2007/503 FastTrack timeo

[Nicolas Williams]

Another approach would be to create an extended crontab distinct from
the normal crontab, requiring an option to the crontab command to
list/update.  But since there is already a commonly supported extension,
that's what we should use.

Also, I don't think we'd want to stop at adding TZ/HOME/PATH/MAILTO if
we were to introduce a separate crontab -- the cost of switching to a
new crontab interface would be high enough that we'd want to make more
improvements in one go.  Plus, the risk that noone would use such a
thing is probably too high (where's the demand?).