Bug#832962: reprotest fails to build properly on jessie

[Robbie Harwood]

Package: reprotest
Followup-For: Bug #832962

So it will need to build against backports because it requires diffoscope.
Most of the build can occur with minor changes to dependencies (vim-common for
xxd, python-tox for tox, fixing version in setup.py).  However, the test suite
does not seem to run happily against python34, which would be needed.

-- System Information:
Debian Release: stretch/sid
  APT prefers testing
  APT policy: (600, 'testing'), (400, 'unstable'), (200, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.8.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)