Registry is working (first cut)

[Ted Zlatanov <tzz@lifelogs.com>]

I consider this a bug-fixing patch to the registry, since it didn't
work at all well before.  I'll feel better knowing a semi-working
version is going into Gnus 5.10.

If you load gnus-registry.el, the following will happen:

- all messages will be tracked to the group where they are spooled,
  copied, or moved.  Deletions are also caught.  Multiple groups (for
  a copy) are OK, only the latest one is caught.

- when you enter a group, the message IDs of all the articles will be
  registered, UNLESS the article is already registered.  Thus,
  multiple copies will not be registered when you enter a group.

NOTE: I'd like to limit this to mail groups only, what's the
"canonical" way?  message-this-is-{news|mail} didn't seem to work when
I tested it.  In the meanwhile, you will get a lot of registered
messages from newsgroups...

- only the short version of the group name is saved, for many reasons

- the registry will be saved in your .newsrc.eld.  I can change that
  if people feel it's too large.  I optimized the format a bit, so it
  should be fast and compact now.

- gnus-registry-split-fancy-with-parent works exactly like
  nnmail-split-fancy-with-parent, just use 

(: gnus-registry-split-fancy-with-parent) 

  in your split-fancy rules.

- gnus-registry-clear can be invoked to clear the registry, if you
  need to.

Have fun with it...

Thanks
Ted