Log message:
py-vmailmgr: add Python 3 support. NFCI for 2.7.

Log message:
Add vmailmgr, a virtual domain manager for qmail.

VMailMgr (short for Virtual MAIL ManaGeR) is a package of programs
designed to manage multiple domains of mail addresses and mailboxes on a
single host. It co-operates with qmail for mail delivery and program
control. It features:

- A password checking interface between qmail-popup and qmail-pop3d
  which replaces the usual checkpassword, as well as an authentication
  module for Courier IMAP, that provide access to the virtual mailboxes
  by one of three methods:
  - IP-based virtual server access (invisible to the POP3 user)
  - username-based access (username-virtualuser)
  - hostname-based access (virtualuser@virtual.host or
    virtualuser:virtual.host)
- CDB-based password tables to speed up access for domains of any size.
- Tools to setup a virtual domain, add and delete individual virtual
  users and aliases, and to change passwords.
- A separate delivery agent that automatically deals with any address
  inside a virtual domain from a single .qmail-default file.