Relicense zsh completion script under zsh license.

Steve agreed some time ago.

contrib/zsh_completion

@@ -13,13 +13,25 b''
 # autoload -U compinit
 # compinit
 #
-# Copyright (C) 2005-6 Steve Borho
-# Copyright (C) 2006-8 Brendan Cully <[e-mail]>
+# Copyright (C) 2005, 2006 Steve Borho <[e-mail]>
+# Copyright (C) 2006, 2007, 2008 Brendan Cully <[e-mail]>
+#
+# Permission is hereby granted, without written agreement and without
+# licence or royalty fees, to use, copy, modify, and distribute this
+# software and to distribute modified versions of this software for any
+# purpose, provided that the above copyright notice and the following
+# two paragraphs appear in all copies of this software.
 #
-# This 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.
+# In no event shall the authors be liable to any party for direct,
+# indirect, special, incidental, or consequential damages arising out of
+# the use of this software and its documentation, even if the authors
+# have been advised of the possibility of such damage.
+#
+# The authors specifically disclaim any warranties, including, but not
+# limited to, the implied warranties of merchantability and fitness for
+# a particular purpose.  The software provided hereunder is on an "as
+# is" basis, and the authors have no obligation to provide maintenance,
+# support, updates, enhancements, or modifications.
 
 emulate -LR zsh
 setopt extendedglob