t7504: document regression: reword no longer calls commit-msg

The `reword` command of an interactive rebase used to call the
commit-msg hooks, but that regressed when we switched to the
rebase--helper backed by the sequencer.

Noticed by Sebastian Schuberth.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7504-commit-msg-hook.sh

@@ -220,4 +220,21 @@ test_expect_success "hook doesn't edit commit message (editor)" '
 
 '
 
+# set up fake editor to replace `pick` by `reword`
+cat > reword-editor <<'EOF'
+#!/bin/sh
+mv "$1" "$1".bup &&
+sed 's/^pick/reword/' <"$1".bup >"$1"
+EOF
+chmod +x reword-editor
+REWORD_EDITOR="$(pwd)/reword-editor"
+export REWORD_EDITOR
+
+test_expect_failure 'hook is called for reword during `rebase -i`' '
+
+	GIT_SEQUENCE_EDITOR="\"$REWORD_EDITOR\"" git rebase -i HEAD^ &&
+	commit_msg_is "new message"
+
+'
+
 test_done