[imp] Patch to empty any folder

[Chuck Hagenbuch]

Quoting "Marcus I. Ryan" <marcus@riboflavin.net>:

> The following patch adds the action "Empty folder(s)" in the Folders
> view.  It deletes and expunges all messages form the given mailbox.
> Created and tested under HEAD.

Committed with a few tweaks, thanks.

-chuck

--
Charles Hagenbuch, <chuck@horde.org>
"A dream which helps you to live your reality with dignity
 and justice is a good dream." - Tariq Ramadan