the service file should only be installed and not enabled because we
share the display-manager.service file with other DMs

handle better shared display-manager.service unit file

Closes: #950390

Fix some issues reported by lintian

See merge request xfce-extras-team/lightdm!3

Fixes: lintian: upstream-metadata-file-is-missing
See-also: https://lintian.debian.org/tags/upstream-metadata-file-is-missing.html

Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html

Fixes: lintian: file-contains-trailing-whitespace
See-also: https://lintian.debian.org/tags/file-contains-trailing-whitespace.html

Apply multi-arch hints

See merge request xfce-extras-team/lightdm!2

* liblightdm-gobject-dev: Drop Multi-Arch: same.
* gir1.2-lightdm-1: Drop Multi-Arch: same.

Closes: #945292

It seems that default behavior changed at some point, making the package
FTBFS because dh_install can't find the gtk-doc folder.

Thanks Moritz Mühlenhoff for the patch

closes: #922160

Backport upstream hide systemd dynamic users fix

See merge request !1