automake: fix automake bug #18485

From https://bugs.gnu.org/18485 (Niels Möller).

Recognise COPYINGv2, COPYINGv3, COPYING.LESSERv2 and COPYING.LESSERv3
as license files; distribute them automatically, similarly to COPYING.
This improves compatibility with other GNU projects, notably GNU GMP.

A regression test has been added alongside the change.

* bin/automake.in: Add the relevant license names to common files and
  licenses list.
* NEWS: Mention this patch.
* t/license-gnulib-names.sh: Add a regression test.
* t/list-of-tests.mk: Register the test above.