opt: relicense to GPLv2+ (from GPLv3+)

Acked by contributors:
Luke-Jr <luke@dashjr.org>:
	 I don't have any objections
Douglas Bagnall <douglas@halo.gen.nz>:
	Fine by me.
Joel Stanley <joel@jms.id.au>:
	Fine with me.
Brad Hards <bradh@frogmouth.net>:
	Ack.

No response from Joey (trivial warning patch) or Andreas Schlick (one
trivial patch, but he also wrote opt_free() (which was a 2 line function).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/opt/LICENSE

-../../licenses/GPL-3
\ No newline at end of file
+../../licenses/GPL-2
\ No newline at end of file

ccan/opt/_info

@@ -52,7 +52,7 @@
  * 	return 0;
  * }
  *
- * License: GPL (v3 or any later version)
+ * License: GPL (v2 or any later version)
  * Author: Rusty Russell <rusty@rustcorp.com.au>
  */
 int main(int argc, char *argv[])

ccan/opt/helpers.c

-/* Licensed under GPLv3+ - see LICENSE file for details */
+/* Licensed under GPLv2+ - see LICENSE file for details */
 #include <ccan/opt/opt.h>
 #include <ccan/cast/cast.h>
 #include <inttypes.h>

ccan/opt/opt.c

-/* Licensed under GPLv3+ - see LICENSE file for details */
+/* Licensed under GPLv2+ - see LICENSE file for details */
 #include <ccan/opt/opt.h>
 #include <string.h>
 #include <errno.h>

ccan/opt/opt.h

-/* Licensed under GPLv3+ - see LICENSE file for details */
+/* Licensed under GPLv2+ - see LICENSE file for details */
 #ifndef CCAN_OPT_H
 #define CCAN_OPT_H
 #include <ccan/compiler/compiler.h>

ccan/opt/parse.c

-/* Licensed under GPLv3+ - see LICENSE file for details */
+/* Licensed under GPLv2+ - see LICENSE file for details */
 /* Actual code to parse commandline. */
 #include <ccan/opt/opt.h>
 #include <string.h>

ccan/opt/private.h

-/* Licensed under GPLv3+ - see LICENSE file for details */
+/* Licensed under GPLv2+ - see LICENSE file for details */
 #ifndef CCAN_OPT_PRIVATE_H
 #define CCAN_OPT_PRIVATE_H
 

ccan/opt/usage.c

-/* Licensed under GPLv3+ - see LICENSE file for details */
+/* Licensed under GPLv2+ - see LICENSE file for details */
 #include <ccan/opt/opt.h>
 #if HAVE_SYS_TERMIOS_H
 #include <sys/ioctl.h>