When running aunpack on .rar files, I would expect it to run unrar
command, but it doesn't…
So whether I installed `unrar-free` or `unrar` package, it's not used.
It only supports rar files if the `rar` package is installed.

See log:

Can't exec "rar": No such file or directory at /usr/bin/aunpack line 1868.
rar: cannot execute - No such file or directory
aunpack: rar ...: non-zero return-code