On VCS-independent ways of identifying commits, and why they are desirable.

No code changes.

Makefile.in

@@ -385,6 +385,7 @@ src: Makefile FRC
 	cd $@ || exit;							\
 	boot=bootstrap-emacs$(EXEEXT);					\
 	[ ! -x "$$boot" ] || boot='';					\
+	echo "VCSWITNESS: $$vcswitness";\
 	$(MAKE) all $(MFLAGS)						\
 	  CC='${CC}' CFLAGS='${CFLAGS}' CPPFLAGS='${CPPFLAGS}'		\
 	  LDFLAGS='${LDFLAGS}' MAKE='${MAKE}' BOOTSTRAPEMACS="$$boot"	\

admin/ChangeLog

@@ -1,3 +1,8 @@
+2014-01-16  Eric S. Raymond  <esr@thyrsus.com>
+
+	* notes/commits: Add a 'graph on VCS-independent ways of
+	identifying commits and the desirability thereof.
+
 2014-01-15  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Fix copyright license notices for Adobe Unicode mapping files.

admin/notes/commits

@@ -45,6 +45,15 @@ Date: 	 Tue, 31 Mar 2009 12:21:20 +0900
     for modern source-control systems with a global log, it's better to
     have something like "Regenerate configure".
 
+(4) (Added in 2014) In commit comments, and ChangLog files, it is best
+    to use ways of identifying revisions that are not dependent on a
+    particular version control system.  (At time of writing Emacs is
+    about to move to its third VCS and another move in the future is
+    not impossible.)  An excellent way to identify commits is by
+    quoting their summary line.  Another is with an action stamp - an
+    RFC3339 date followed by ! followed by the committer's email - for
+    example, "2014-01-16T05:43:35Z!esr@thyrsus.com". Often, "my
+    previous commit" will suffice.
 
 Followup discussion:
 http://lists.gnu.org/archive/html/emacs-devel/2010-01/msg00897.html