Using `libtoolize --copy --ltdl' was not preserving timestamps, so

Using `libtoolize --copy --ltdl' was not preserving timestamps, so
parts of the autoconf bootstrap would be rerun spuriously after
the files had been copied into the source tree:

* libtoolize.m4sh (TAR): New default tar command.
(func_copy_cb): Move the core copying internals to here, using
$TAR to transfer files if possible when --copy was specified.
(func_copy): Adjust to call func_copy_cb.
Reported by Jeff Squyres <jsquyres@lam-mpi.org>