An archive for the last 30 days

Hi. I've often found the archive index to be somewhat unintuitive. If I'm following a list, I want a link that I can hit that will show me the last 30 days of activity, rather than making me change that link every month.

This is a patch that implements a new archive -- in addition to the months ones, there is a new one called "last30" that will show the last 30 days of activity on the list.

You need to run "bin/arch --last30 listname" in order to prune out the old messages from the archive, but it is fast and efficient. You can run this in a cron script that goes once a day or something.