The current algorithm creates attributes with null values for packages
with no source in a variant of MELPA. Though will satify dependencies
they produce no files, and though a build that transitively depends on
one them will be successful, Emacs won't find them and any code
depending on them won't work.

The solution with minimal code change would have been filtering the
list of results from melpaDerivation by comparing the value against
null, but that leads to an infinite recursion.

This commit also moves legacy renames from the shared to the unstable
set, as the corresponding null value elements won't exist in the
stable set anymore.

The test used for the problem was:

  $ nix-build --show-trace ./default.nix -A emacs26Packages.melpaStablePackages.findr
  error: expression does not evaluate to a derivation (or a set or list of those)

The expected output, obtained with this commit is:

  $ nix-build --show-trace ./default.nix -A emacs26Packages.melpaStablePackages.findr
  error: attribute 'findr' in selection path 'emacs26Packages.melpaStablePackages.findr' not found

'toString false' results in an empty string, which, in this context,
is a syntax error. Use boolToString instead.

Fixes #86160

(cherry picked from commit c0a838d)

(cherry picked from commit 660d284)

[20.03] nixos/gitlab: Fix services.gitlab.enableStartTLSAuto

[20.03] signal-desktop: 1.33.3 -> 1.33.4 (backport)

See
https://about.gitlab.com/releases/2020/04/14/critical-security-release-gitlab-12-dot-9-dot-3-released/
for details.
(cherry-picked from commit d190292)

- CVE-2020-6071
- CVE-2020-6072
- CVE-2020-6073
- CVE-2020-6077
- CVE-2020-6078
- CVE-2020-6079

Buildsystem switched to Meson+Ninja.

(cherry picked from commit 18f3661)

…ll-pkgs

emacs-modes: build MELPA package sets without null packages

While it's already possible to invoke `update-data` with the `--rev`
argument, one still needs to run all later phases manually.

Fix this, by having `update-all` also accept a `--rev` argument, and
pass it down to `update-data`.

Also, make the help text a bit more usable, by suggesting the usual
versioning scheme used these times.

(cherry picked from commit 191c2c67a409ae8cf3d3bee7811a7b10397efe81)

(cherry picked from commit f7ddd30bef15238d6d9a12f48408d38571944d85)

(cherry picked from commit c86c77be0cf45023586e7252bfb05238ae6d38db)

`bundix -l` doesn't work, as it treats bundler's warning about upgrading
the lockfile version as an error, so invoke `bundle lock` manually.

(cherry picked from commit c7d47ce06fba88341e2d072379013414be4ee2e1)

(cherry picked from commit 9d73d28)

https://github.com/elementary/gala/releases/tag/3.3.1
(cherry picked from commit f5ddad7)

These .desktop files set InitialPreference>1 which will override other
associations even the .desktop appears first in XDG_DATA_DIRS. This
applies to:

- org.kde.kate.desktop
- org.kde.kwrite.desktop
- kfmclient_html.desktop
- okularApplication_txt.desktop

Fixes #86137

(cherry picked from commit b3f8126)