*: 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/printf.tests

@@ -1,6 +1,6 @@
 #!/bin/sh
 # Copyright 2008 by Denys Vlasenko
-# Licensed under GPL v2, see file LICENSE for details.
+# Licensed under GPLv2, see file LICENSE in this source tree.
 
 . ./testing.sh