Make sure lockfiles are unlocked when dying on SIGPIPE

We cleaned up lockfiles upon receiving the usual suspects HUP, TERM, QUIT
but a wicked user could kill us of asphyxiation by piping our output to a
pipe that does not read.  Protect ourselves by catching SIGPIPE and clean
up the lockfiles as well in such a case.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

lockfile.c

@@ -140,6 +140,7 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
 			signal(SIGHUP, remove_lock_file_on_signal);
 			signal(SIGTERM, remove_lock_file_on_signal);
 			signal(SIGQUIT, remove_lock_file_on_signal);
+			signal(SIGPIPE, remove_lock_file_on_signal);
 			atexit(remove_lock_file);
 		}
 		lk->owner = getpid();

t/t3600-rm.sh

@@ -251,4 +251,21 @@ test_expect_success 'refresh index before checking if it is up-to-date' '
 
 '
 
+test_expect_success 'choking "git rm" should not let it die with cruft' '
+	git reset -q --hard &&
+	H=0000000000000000000000000000000000000000 &&
+	i=0 &&
+	while test $i -lt 12000
+	do
+	    echo "100644 $H 0	some-file-$i"
+	    i=$(( $i + 1 ))
+	done | git update-index --index-info &&
+	git rm -n "some-file-*" | :;
+	test -f .git/index.lock
+	status=$?
+	rm -f .git/index.lock
+	git reset -q --hard
+	test "$status" != 0
+'
+
 test_done