[VM] Don't use the mailbox as an address book

[Uday S Reddy]

Can I also gently remind everybody that it is a bad practice to use your
mailbox as an address book?  If you try to locate an old message from
somebody in your mailbox and do a `reply' instead of composing a new
message, your message gets tagged as a response to an old message, possibly
a huge thread, and your recipients will fail to notice it.

Notice how Terry's message is buried deep inside a thread started on Aug 5
on Google Groups:

http://groups.google.com/group/gnu.emacs.vm.info/browse_thread/thread/bb4adb5c8c568490/c4c33369e98b0ce5?lnk=gst&q=terry+jones#c4c33369e98b0ce5

In due course, I intend to add some functions to VM to make this convenient.

Detaching such burried messages in existing threads is a much harder
problem.  But I have been thinking about it too.

Cheers,
Uday