IUCr forums

A couple of modifications have been introduced, one at Gervais' request and the other because it seemed useful:

* notify_moderators: sends an email (or private message) to a board moderator when a new post arrives for moderation
* prime_notify: includes the text of a post in the email notification sent to users

I have also added the AUTOMOD mod, which is designed to automate future mod additions. That will help in future (though the tool may not be able to install all user mods).