Bug#223019: File-roller should tell the user directly if executables are not installed

[Clément Stenac]

Hello,

This has been improved in newer upstream releases by adding a "Archive
format not supported" message.

Altough it's not yet perfect as it does not really explain that it is
because the executable is not installed, I think it's ok for now.

Additionnaly, I'll add a note in README.Debian for file-roller explaining
this better.

-- 
Clément