Bug#797113: libdvd-pkg doesn't respect APT's proxy settings when downloading libdvdcss

[Austin English]

Package: libdvd-pkg
Version: 1.3.99-1-1
Severity: important

Dear Maintainer,

   * What led up to the situation?
   Attempting to add libdvd-pkg to Tails, which uses an HTTP proxy when building its image.

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

echo > libdvd-pkg-debconf << _EOF
debconf libdvd-pkg/post-invoke_hook-install boolean true
_EOF
debconf-set-selections libdvd-pkg-debconf

apt-get --yes install dh-autoreconf libdvd-pkg

   * What was the outcome of this action?
wget --tries=3 --timeout=40 --read-timeout=40 --continue -O libdvdcss_1.3.99.orig.tar.bz2 \
          http://download.videolan.org/pub/libdvdcss/1.3.99/libdvdcss-1.3.99.tar.bz2 \
        || uscan --noconf --verbose --rename --destdir=/usr/src/libdvd-pkg --check-dirname-level=0 --force-download --download-current-version /usr/share/libdvd-pkg/debian
--2015-08-27 20:12:40--  http://download.videolan.org/pub/libdvdcss/1.3.99/libdvdcss-1.3.99.tar.bz2
Resolving download.videolan.org (download.videolan.org)... [Aug 27 20:12:40] PERROR torsocks[17749]: socks5 libc connect: Connection refused (in socks5_connect() at socks5.c:185)
failed: Non-recoverable failure in name resolution.
wget: unable to resolve host address `download.videolan.org'
/bin/sh: 3: uscan: not found
make: *** [get-orig-source] Error 127

   * What outcome did you expect instead?
I expect the download to use apt's proxy, and libdvdcss to build built.

b43-firmware-installer does something similar, and works. In their postinst, they do:
# use apt proxy
APT_PROXIES=$(apt-config shell \
http_proxy Acquire::http::Proxy \
https_proxy Acquire::https::Proxy \
ftp_proxy Acquire::ftp::Proxy \
)

if [ -n "$APT_PROXIES" ]; then
        eval export $APT_PROXIES
fi

I tried adapting to libdvd-pkg-1.3.99-1/libdvdcss/debian/rules, but it didn't work.
May be useful as a starting point for someone:
        @APT_PROXIES=$(apt-config shell \
        http_proxy Acquire::http::Proxy \
        https_proxy Acquire::https::Proxy \
        ftp_proxy Acquire::ftp::Proxy \
        )

        if [ -n "$(APT_PROXIES)" ]; then
            eval export "$(APT_PROXIES)"
        fi

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.1.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages libdvd-pkg depends on:
ii  build-essential        12.1
ii  debconf [debconf-2.0]  1.5.57
ii  debhelper              9.20150811
ii  devscripts             2.15.8
ii  dh-autoreconf          10
ii  wget                   1.16.3-3

Versions of packages libdvd-pkg recommends:
ii  libcap2-bin  1:2.24-11

libdvd-pkg suggests no packages.

-- debconf information:
  libdvd-pkg/upgrade:
* libdvd-pkg/post-invoke_hook-install: true
  libdvd-pkg/title_b-i:
  libdvd-pkg/build: true
* libdvd-pkg/first-install:
  libdvd-pkg/post-invoke_hook-remove: false
  libdvd-pkg/title_u: