Force usage of gtar

Index: scripts/miscellaneous/private/tar_is_bsd.m
--- scripts/miscellaneous/private/tar_is_bsd.m.orig
+++ scripts/miscellaneous/private/tar_is_bsd.m
@@ -39,13 +39,13 @@ function out = tar_is_bsd ()
 
   ## BSD tar needs to be handled differently from GNU tar
   persistent cache;
-  if (isempty (cache))
+  if (0)
     [status, tar_ver_str] = system ("tar --version");
     if (status)
       error ("tar: Failed executing tar --version (status = %d)", status);
     endif
     cache = ! isempty (regexp (tar_ver_str, "bsdtar"));
   endif
-  out = cache;
+  out = 0;
 
 endfunction
