maint: add rule to ensure that our commit hook copies are up to date

* Makefile.am (check-git-hook-script-sync): New rule -- not used
anywhere, because it depends on having very recent git.
* scripts/git-hooks/pre-applypatch: New file.

Makefile.am

@@ -155,3 +155,17 @@ THANKS: THANKS.in Makefile.am .mailmap thanks-gen .version
 	  echo;								\
 	  printf ';; %s\n' 'Local Variables:' 'coding: utf-8' End:;	\
 	} > $@-t && mv $@-t $@
+
+# Some of our git hook scripts are supposed to be identical to git's samples.
+# See if they are still in sync.
+.PHONY: check-git-hook-script-sync
+check-git-hook-script-sync:
+	@fail=0;							\
+	t=$$(mktemp -d)							\
+	  && cd $$t && git init -q && cd .git/hooks			\
+	  && for i in pre-commit pre-applypatch applypatch-msg; do	\
+	       diff $(abs_top_srcdir)/scripts/git-hooks/$$i $$i.sample	\
+		 || fail=1;						\
+	     done;							\
+	rm -rf $$t;							\
+	test $$fail = 0

scripts/git-hooks/pre-applypatch

@@ -0,0 +1,14 @@
+#!/bin/sh
+#
+# An example hook script to verify what is about to be committed
+# by applypatch from an e-mail message.
+#
+# The hook should exit with non-zero status after issuing an
+# appropriate message if it wants to stop the commit.
+#
+# To enable this hook, rename this file to "pre-applypatch".
+
+. git-sh-setup
+test -x "$GIT_DIR/hooks/pre-commit" &&
+	exec "$GIT_DIR/hooks/pre-commit" ${1+"$@"}
+: