This adds LGPL and GFDL texts from the GNU web site and updates the GPL
one:

  COPYING: https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
  COPYING.LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt
  COPYING.GFDL: https://www.gnu.org/licenses/old-licenses/fdl-1.1.txt

The update to the GPL text is purely cosmetic. However, shipping the
exact same file as GNU publishes may help distros that deduplicate the
license texts or hardlink duplicates.