Can no longer have more than one imap folder with wastebin property

[Andrew Bird]

In the past it was possible to have more than one imap folder with the 'Wastebin' folder type. For me it was useful to add to my server filtered Spam folder, so allowing the right click 'Empty Wastebin' option.

In this version (3.16.0) setting the `Wastebin' folder type promotes it to be the Trash folder, demotes the previous Trash folder and removes the 'Wastebin' folder type from it. The problem with this is that folder contents without the 'Wastebin' property have to be deleted and are sent to the real Trash folder not immediately removed. Of course that means in my case that spam messages are intermixed with proper but perhaps no longer required messages, making recovery of those somewhat confusing.

$ lsb_release -rd
Description: Ubuntu 18.04.1 LTS
Release: 18.04

$ apt-cache policy claws-mail
claws-mail:
  Installed: 3.16.0-1
  Candidate: 3.16.0-1
  Version table:
 *** 3.16.0-1 500
        500 http://gb.archive.ubuntu.com/ubuntu bionic/universe i386 Packages
        100 /var/lib/dpkg/status