message registry for Gnus

[Ted Zlatanov <tzz@lifelogs.com>]

So, I've been thinking about a message registry.  What will it do?

- track messages by ID

- associate a Lisp structure (probably a list, hashes are too new?)
  with a message ID

- allow every customer package to hook into the relevant functions

- store the registry in a separate file or in the newsrc.eld?

Before I start coding, I wanted to sort of look around and see what
people think.

In the context of spam.el, the registry will be used to track when a
message changes groups, or is processed by a spam/ham processor.  That
way, we can see if a message that will be registered as spam with
ifile now has been registered as ham with Bogofilter, for instance,
and reverse the Bogofilter registration before registering with ifile.

In Gnus terms, what are the basic message transfer functions?

- message copy

- message move

- new message spooling

- old message respooling

What else?

Is this easily doable?

Thanks
Ted