debian: Update copyright files to point the correct common license files

debian: Update copyright files to point the correct common license files

This fixes the Lintian warning:

   The copyright file refers to the versionless symlink in
   /usr/share/common-licenses for the full text of the GPL, LGPL, or GFDL
   license, but the package does not appear to allow distribution under
   later versions of the license. This symlink will change with each
   release of a new version of the license and may therefore point to a
   different version than the package is released under. debian/copyright
   should instead refers to the specific version of the license that the
   package references.

   For example, if the package says something like "you can redistribute it
   and/or modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; version 2 dated June, 1991,"
   the debian/copyright file should refer to
   /usr/share/common-licenses/GPL-2, not /GPL.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>