Added copyleft header.

+dnl This file is part of GNU mailutils.
+dnl Copyright (C) 2003 Free Software Foundation, Inc.
+dnl
+dnl GNU Mailutils is free software; you can redistribute it and/or modify
+dnl it under the terms of the GNU General Public License as published by
+dnl the Free Software Foundation; either version 2, or (at your option)
+dnl any later version.
+dnl 
+dnl GNU Mailutils is distributed in the hope that it will be useful,
+dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
+dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+dnl GNU General Public License for more details.
+dnl 
+dnl You should have received a copy of the GNU General Public License
+dnl along with GNU Mailutils; if not, write to the Free Software
+dnl Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA  
+dnl
 AC_DEFUN(MU_CHECK_TLS,
 [
  if test "x$WITH_GNUTLS" = x; then