license of Makefile.in

[Ben Pfaff]

While packaging Autoconf 2.69 for Debian, I am trying to update
the copyright information in the package using the new Debian
copyright format here:
          http://www.debian.org/doc/packaging-manuals/copyright-format/1.0/

In the process, I'm looking at each file in Autoconf to
understand its licensing.  One file that has a confusing license
is Makefile.in.  It contains one license at the top, output by
Automake:

    # Copyright (C) 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002,
    # 2003, 2004, 2005, 2006, 2007, 2008, 2009  Free Software Foundation,
    # Inc.
    # This Makefile.in is free software; the Free Software Foundation
    # gives unlimited permission to copy and/or distribute it,
    # with or without modifications, as long as this notice is preserved.

    # This program is distributed in the hope that it will be useful,
    # but WITHOUT ANY WARRANTY, to the extent permitted by law; without
    # even the implied warranty of MERCHANTABILITY or FITNESS FOR A
    # PARTICULAR PURPOSE.

with another license below it copied from Makefile.am:

    # Copyright (C) 1999-2004, 2006-2012 Free Software Foundation, Inc.

    # This program is free software: you can redistribute it and/or modify
    # it under the terms of the GNU General Public License as published by
    # the Free Software Foundation, either version 3 of the License, or
    # (at your option) any later version.

    # This program is distributed in the hope that it will be useful,
    # but WITHOUT ANY WARRANTY; without even the implied warranty of
    # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    # GNU General Public License for more details.

    # You should have received a copy of the GNU General Public License
    # along with this program.  If not, see <http://www.gnu.org/licenses/>.

My guess is that the overall license of Makefile.in is then the
conjunction of the two, that is, GPLv3+.  At any rate, the double
license is somewhat confusing, so I'd like to hear feedback in
case I'm wrong.

Thanks,

Ben.