Standardize license text and switch to GPLv3 or later.

etc/grep.txt

@@ -91,8 +91,8 @@ COPYING PERMISSIONS:
 
     This document 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 2 of the License, or
-    (at your option) any later version.
+    the Free Software Foundation; either version 3, 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
@@ -100,8 +100,9 @@ COPYING PERMISSIONS:
     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, write to the Free Software
-    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+    along with this program; see the file COPYING.  If not, write to
+    the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+    Boston, MA 02110-1301 USA.
 
 
 ;;; Local Variables: