*: make GNU licensing statement forms more regular

This change retains "or later" state! No licensing _changes_ here,
only form is adjusted (article, space between "GPL" and "v2" and so on).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

testsuite/all_sourcecode.tests

@@ -2,7 +2,7 @@
 
 # Tests for the sourcecode base itself.
 # Copyright 2006 by Mike Frysinger <vapier@gentoo.org>
-# Licensed under GPL v2, see file LICENSE for details.
+# Licensed under GPLv2, see file LICENSE in this source tree.
 
 [ -n "$srcdir" ] || srcdir=$(pwd)
 . ./testing.sh