dist: 'make set-timestamps' cleanup

* Makefile (set-timestamps): Use git's tformat rather than format,
to port to strict POSIX hosts where `` output in shell scripts
cannot end in a non-newline.  Use git diff --quiet rather than git
diff --name-only, as it's simpler.  Use touch -c for safety, and
-m to avoid setting last-access time, which we don't care about.
Diagnose files that don't match repository.
* NEWS: Document this.

Makefile

@@ -472,16 +472,17 @@ public:		check check_public check_time_t_alternatives \
 # and if the files have not changed since then.
 # This uses GNU 'touch' syntax 'touch -d@N FILE',
 # where N is the number of seconds since 1970.
-# If git or GNU 'touch' is absent, do nothing.
+# If git or GNU 'touch' is absent, do nothing and fail.
 set-timestamps:
-		-TZ=UTC0 && export TZ && files=`git ls-files` && \
+		-files=`git ls-files` && \
 		touch -d @1 test.out && rm -f test.out && \
 		for file in $$files; do \
-		  test -z "`git diff --name-only $$file`" || continue; \
-		  cmd="touch -d @`git log -1 --format='format:%ct' $$file \
-			` $$file" && \
-		  echo "$$cmd" && \
-		  $$cmd || exit; \
+		  if git diff --quiet $$file; then \
+		    time=`git log -1 --format='tformat:%ct' $$file` && \
+		    touch -cmd @$$time $$file; \
+		  else \
+		    echo >&2 "$$file: warning: does not match repository"; \
+		  fi || exit; \
 		done
 
 # The zics below ensure that each data file can stand on its own.

NEWS

@@ -28,6 +28,8 @@ Unreleased, experimental changes
     done differently, and tags would either not have a simple name or
     not exactly match what was released.
 
+    'make set-timestamps' is now simpler and a bit more portable.
+
 
 Release 2013e - 2013-09-19 23:50:04 -0700