qpdecode

I recommend putting this in your .emacs, after preloading the
appropriate packages or using eval-after-load:

        (autoload 'qpdecode-decode-message "qpdecode" nil t)
        (define-key vm-mode-map "D" 'qpdecode-decode-message)
        (define-key rmail-mode-map "D" 'qpdecode-decode-message)

TODO: Recompute or remove Content-MD5 header?
The gnus article mode hacking doesn't seem to work quite right yet.