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/data/acl-command b/perl/t/data/acl-command
index b7c3066..bdf106a 100755
--- a/perl/t/data/acl-command
+++ b/perl/t/data/acl-command
@@ -5,10 +5,9 @@
 # failure, or reports an error based on whether the second argument is
 # success, failure, or error.
 #
-# Written by Russ Allbery <eagle@eyrie.org>
 # Copyright 2016 Russ Allbery <eagle@eyrie.org>
 #
-# See LICENSE for licensing terms.
+# SPDX-License-Identifier: MIT
 
 set -e