[Dovecot] Lazy expunge plugin

There's now a plugin called lazy_expunge in CVS. Instead of EXPUNGE expunging the mails directly, they're moved to a mailbox with same name in another namespace where user can still copy the mails back. Also DELETEd mailboxes are moved to another namespace.

See http://wiki.dovecot.org/Plugins/Lazyexpunge for more information.

This is similar to Cyrus's two phase expunge: http://www-uxsup.csx.cam.ac.uk/~dpc22/cyrus/two_phase_expunge.html