Should support mail notification of new and changed pages.

  Hmm, should be easy to implement this.. it runs as a svn post-coommit hook
  already, so just look at the userdb, svnlook at what's changed, and send
  mails to people who have subscribed.

  A few details:
  1. [[Joey]] mentioned that being able to subscribe to globs as well as
     explicitly named pages would be desirable.
  2. I think that since we're using Perl on the backend, being able to
     let users craft their own arbitrary regexes would be good.

     Joey points out that this is actually a security hole, because Perl
     regexes let you embed (arbitrary?) Perl expressions inside them.  Yuck!

(This is not actually true unless you "use re 'eval';", without which
(?{ code }) is disabled for expressions which interpolate variables.
See perldoc re, second paragraph of DESCRIPTION. It's a little iffy
to allow arbitrary regexen, since it's fairly easy to craft a regular
expression that takes unbounded time to run, but this can be avoided
with the use of alarm to add a time limit. Something like

    eval { # catches invalid regexen
      no re 'eval'; # to be sure
      local $SIG{ALRM} = sub { die };
      alarm(1);
      ... stuff involving m/$some_random_variable/ ...
      alarm(0);
    };
    if ($@) { ... handle the error ... }

should be safe. --[[WillThompson]])

     It would also be good to be able to subscribe to all pages except discussion pages or the SandBox: `* !*/discussion !sandobx`, maybe --[[Joey]]

  3. Of course if you do that, you want to have form processing on the user
     page that lets them tune it, and probably choose literal or glob by
     default.

     I think that the new globlist() function should do everything you need.
     Adding a field to the prefs page will be trivial --[[Joey]]

  The first cut, I suppose, could use one sendmail process to batch-mail all
  subscribers for a given page.  However, in the long run, I can see users
  demanding a bit of feature creep:

  4. Each user should be able to tune whether they see the actual diff parts or
     not.
  5. Each user should be able to set a maximum desired email size.
  6. We might want to support a user-specified shibboleth string that will be
     included in the email they receive so they can easily procmail the messages
     into a folder.

  --[[BrandenRobinson]]

  I'm deferring these nicities until there's some demonstrated demand
  --[[Joey]].

[[todo/done]]
