- Drop all dh_sphinxdoc workarounds; will switch to dh_linktree.
- Avoid debian/*.install files and write code that will work for all
  available translations.
- Don't include '.$lang' in the filenames of the translated HTML.
- Other simplifications and minor corrections.

Thanks to Ian Jackson for help with this.

The verbose builds change and the changelog/NEWS change will apply to
a large number of packages.

    Wording: Sean Whitton <spwhitton@spwhitton.name>
    Seconded: David Bremner <bremner@debian.org>
    Seconded: Ian Jackson <ijackson@chiark.greenend.org.uk>
    Closes: #628515

    Wording: Sean Whitton <spwhitton@spwhitton.name>
    Seconded: Holger Levsen <holger@layer-acht.org>
    Seconded: Bill Allombert <ballombe@debian.org>
    Closes: #886258