git-gui: Make the copyright notice serve double duty.

The copyright notice we display in the about dialog should be the same
as the one at the top of our source code.  By putting the copyright
notice that appears at the top of our source code into a global variable
rather than a comment we can trivially make them the same at all times.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui

@@ -2,10 +2,15 @@
 # Tcl ignores the next line -*- tcl -*- \
 exec wish "$0" -- "$@"
 
-# Copyright (C) 2006 Shawn Pearce, Paul Mackerras.  All rights reserved.
-# This program is free software; it may be used, copied, modified
-# and distributed under the terms of the GNU General Public Licence,
-# either version 2, or (at your option) any later version.
+set copyright {
+Copyright © 2006 Shawn Pearce, Paul Mackerras.
+
+All rights reserved.
+
+This program is free software; it may be used, copied, modified
+and distributed under the terms of the GNU General Public Licence,
+either version 2, or (at your option) any later version.
+}
 
 set appname [lindex [file split $argv0] end]
 set gitdir {}
@@ -2160,7 +2165,7 @@ proc do_commit {} {
 }
 
 proc do_about {} {
-	global appname
+	global appname copyright
 
 	set w .about_dialog
 	toplevel $w
@@ -2179,11 +2184,7 @@ proc do_about {} {
 
 	label $w.desc \
 		-text "$appname - a commit creation tool for Git.
-
-Copyright © 2006 Shawn Pearce, Paul Mackerras
-
-Use and redistribute under the terms of the
-GNU General Public License, v. 2.0 or later." \
+$copyright" \
 		-padx 5 -pady 5 \
 		-justify left \
 		-anchor w \