t3406: modernize style

Update the following:

 - Quote 'setup'
 - Remove blank lines within test case body
 - Use test_commit instead of custom quick_one
 - Create branch "topic" from tag created by test_commit

Signed-off-by: Martin von Zweigbergk <martinvonz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3406-rebase-message.sh

@@ -4,27 +4,17 @@ test_description='messages from rebase operation'
 
 . ./test-lib.sh
 
-quick_one () {
+test_expect_success 'setup' '
-	echo "$1" >"file$1" &&
+	test_commit O fileO &&
-	git add "file$1" &&
+	test_commit X fileX &&
-	test_tick &&
+	test_commit A fileA &&
-	git commit -m "$1"
+	test_commit B fileB &&
-}
+	test_commit Y fileY &&
 
-test_expect_success setup '
+	git checkout -b topic O &&
-	quick_one O &&
+	git cherry-pick A B &&
-	git branch topic &&
+	test_commit Z fileZ &&
-	quick_one X &&
-	quick_one A &&
-	quick_one B &&
-	quick_one Y &&
-
-	git checkout topic &&
-	quick_one A &&
-	quick_one B &&
-	quick_one Z &&
 	git tag start
-
 '
 
 cat >expect <<\EOF
@@ -34,12 +24,10 @@ Committed: 0003 Z
 EOF
 
 test_expect_success 'rebase -m' '
-
 	git rebase -m master >report &&
 	sed -n -e "/^Already applied: /p" \
 		-e "/^Committed: /p" report >actual &&
 	test_cmp expect actual
-
 '
 
 test_expect_success 'rebase --stat' '