Replace unrar-free with unar
Originally created by Tails on #5838 (Redmine)
Unrar-free is working pretty badly and fails to open many .rar archives in Tails. It has tons of Debian bugs: https://bugs.debian.org/unrar-free.
Next thing to do: wait for Tails to be based on Jessie.
When we ship file-roller 3.6 or newer, we should stop installing
unrar-free
as unar
will be used instead. Unfortunately, Wheezy will
have 3.4, so that will be for Jessie.
See have archive manager support rar again (#5592 (closed)) for details.