bug#58734: installer: backtrace page in final step

[Mathieu Othacehe]

> +  (error 'fake)
>    (installer-log-line "running command ~s" command)
>    (define result (run-external-command-with-line-hooks
>                    (list %display-line-hook) command

Fixed with bf5e78d59fcb188d0bce02d93c93d06069178837.

Thanks,

Mathieu