tar bootstrap goodies that are not in gnulib bootstrap

[Paul Eggert]

When we used the latest gnulib bootstrap with GNU tar,
it turns out that we lost some functionality that was in the GNU
tar bootstrap.  Sergey caught this just before GNU tar 1.24
was released.  The missing functionality has to do with tar's
need for paxutils as well as for gnulib.

Gary, can you please look into that with respect with
your proposed replacement to the bootstrap script?
Thanks.

Here's the commit containing the patch that we needed to
apply to gnulib bootstrap to get it to work again with GNU tar:

http://git.savannah.gnu.org/cgit/tar.git/commit/?id=983113b140dbb540923a3112fa27e9f508ff70c5