Add SPDX-License-Identifier headers

Add SPDX-License-Identifier headers to all substantial source files.
Collapse copyright years.  Add some Emacs configuration for files
where the copyright notice is at the end.  Add a test that every
file has SPDX-License-Identifier.

1 files changed, 1 insertions, 2 deletions

diff --git a/perl/t/verifier/external.t b/perl/t/verifier/external.t
index d1438de..2b725bd 100755
--- a/perl/t/verifier/external.t
+++ b/perl/t/verifier/external.t
@@ -2,10 +2,9 @@
 #
 # Tests for the external wallet ACL verifier.
 #
-# Written by Russ Allbery <eagle@eyrie.org>
 # Copyright 2016 Russ Allbery <eagle@eyrie.org>
 #
-# See LICENSE for licensing terms.
+# SPDX-License-Identifier: MIT
 
 use strict;
 use warnings;