Additional suggestions are welcome, as if this plugin isn't
complicated enough.  :-)

-- (Suggested by Phil Grainger)  The Folder Table part of the proon
   form is a bit daunting.  If someone has a lot of folders, they
   probably don't want to automatically prune most of them anyhow.  An
   interface that showed just the folders of interest for pruning (and
   allowing additions) would be simpler, especially for technical
   novices.  I think it might be a good alternative to the current
   Folder Table UI, maybe having a novice and advanced mode for
   displaying and manipulating that information.

-- (Suggested by Jeff Smith)  Allow pruning into other folders besides
   Trash.  He envisions using this to do a simple hierarchical
   storage management of his messages.  Recent messages are in INBOX,
   messages more than a month old go to a folder like INBOX.200507.
   He might then manually put really old folders offline.  Moving to a
   (different-from-Trash) existing folder maybe just needs a column
   with a folder name drop-down for the destination.  Creating a new
   folder with some automatic naming scheme is a bit trickier unless
   it's limited to a small number of fixed schemes (e.g., the by-month
   example).
