also print apt-get --version output with --debug

mmdebstrap

@@ -1545,6 +1545,8 @@ sub setup {
         $ENV{"APT_CONFIG"} = "$tmpfile";
     }
     if ($verbosity_level >= 3) {
+        0 == system('apt-get', '--version')
+          or error "apt-get --version failed: $?";
         0 == system('apt-config', 'dump') or error "apt-config failed: $?";
         debug "content of $tmpfile:";
         copy($tmpfile, \*STDERR);