Bug#926194: e2wm/emacs-window-layout: unintended dist-upgrade dependency resolution due to missing "emacsen" dependency if installed together with emacs25-lucid

[Axel Beckert <abe@debian.org>]

Package: e2wm
Version: 1.4-1
Severity: serious
Control: affects -1 + emacs-lucid emacs25-lucid
Control: clone -1 -2
Control: reassign -2 emacs-window-layout
Control: found -2 emacs-window-layout/1.4

Dear Maintainer,

if I upgrade a machine with emacs25-lucid and e2wm or
emacs-window-layout installed from e.g. Stretch to Buster, I can't
upgrade emacs25-lucid to emacs-lucid, because e2wm/emacs-window-layout
in Buster only depend on "emacs25-nox | emacs25", but not on any of the
generic virtual emacs packages like "emacs" or "emacsen".

Historically that worked, because emacs25-lucid did provide also
"emacs25" in Stretch, but since it's just a transitional package in
Buster, it no more provides emacs25 but depends on emacs-lucid which
itself only provides the current virtual emacs packages "emacs" and
"emacsen" (plus some other more generic things like "editor" which are
not relevant in this case).

So please change the dependencies to at least include "emacs" or even
better — because backwards compatible — "emacsen".

P.S.: IMHO this is release-critical because there is a dependency
missing which mislead both apt as well as aptitude on dist-upgrades:

* apt wants to replace emacs25-lucid (a lean GUI variant) with
  the non-gui variant emacs25-nox (which is not intended at all), and,

* depending on settings, aptitude suggests to not upgrade emacs25-lucid
  or to replace it with emacs25-nox as first suggestion, too:

  The following packages have unmet dependencies:
   emacs-lucid : Conflicts: emacs-nox but 1:26.1+1-3.2 is to be installed
   emacs-nox : Conflicts: emacs-lucid but 1:26.1+1-3.2 is to be installed
  The following actions will resolve these dependencies:

       Remove the following packages:
  1)     emacs25-lucid [25.1+1-4+deb9u1 (now)]

       Keep the following packages at their current version:
  2)     emacs-lucid [Not Installed]

On just "apt upgrade" or "aptitude safe-upgrade" both keep back
emacs25-lucid.

All these dependency resolution issues have no real reason except
missing (uptodate alternative) dependencies.